Trailer Wiring Diagrams

6-Pole Diagram

6-Pole Diagram

Trailer Wiring Connectors

Various connectors are available from four to seven pins that allow for the transfer of power for the lighting as well as auxiliary functions such as an electric trailer brake controller, backup lights, or a 12V power supply for a winch or interior trailer lights. Choose a connector that has the required number of pins for the functions required for your trailer. If the connector is under the vehicle, you will want to use a mounting bracket to attach it to the vehicle. This will help prevent damage that may occur if the connector is left dangling.

Trailer Wiring Color Code
ConnectorFunctionColorSuggested Minimum Wire GaugeWhere To Attach - Vehicle SideWhere To Attach - Trailer Side
4 Way & 5 Way6 Way & 7 Way
7 Way6 Way5 Way4 WayRight TurnGreen1816Right turn of vehicle's wiring harnessTrailer's right turn signal
Left TurnYellow1816Left turn of vehicle's wiring harnessTrailer's left turn signal
GroundWhite1612Vehicle ground point - metal, uncoated, rustproofTrailer ground point - metal, uncoated, rustproof
Tail / MarkerBrown1816Taillight of vehicle's wiring harnessTrailer's taillights
Brake*Blue1812Electric brake control, power for brakesBreak away switch
BatteryRed (or Black)12Fuse block or FUSED battery LeadBreak away kit, interior lights and battery charger.
Back UpPurple16Back up circuit of vehicle's wiring harnessBack up lights (if available) / Hydraulic coupler.

This chart is a typical guide, wire colors may vary based on manufacturers. Use a circuit tester to verify connections.

*NOTE: The fifth connection is sometimes used on 5-ways to power a reverse lockout on trailers with surge brakes. When this is the case, the lockout should be connected to the backup light circuit of the tow vehicle.

4-Way Connectors

4-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake lights) plus one pin is provided for a ground wire. Most standard light duty trailers will use a 4-pole flat connector.

5-Way Connectors

5-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake) and, besides the ground, one pin is available to provide support for another function. Typically the 5-Way Flat is used for trailers with surge brakes or hydraulic brakes. The additional wire is tapped into the backup lights to disengage the hydraulic trailer coupler (actuator) when the vehicle is reversing, thus turning off the trailer's brakes.

6-Way Connectors

6-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake). The ground and two extra pins are available to provide two additional functions, typically for electric brakes and 12 volt "hot" lead. The 6-way round connectors are very common on horse trailers. The 6-way square connectors are more common on campers.

6-Way Vehicle Diagram

Note: In some applications, the black battery power connection and the blue brake controller output connection are reversed.

7-Way Connectors

Aside from the three main lighting functions, additional pins for electric brakes, a 12 volt "hot" lead, and backup lights are available. There are two types of 7-way connectors. One has flat pins, which are often referred to as blades. The other has round pins. The round pin style is very rare. The RV style 7-way with flat pins (or blades) is very common. It is often found on newer trucks and SUVs that come equipped from the factory with a trailer hitch.

7-Way Trailer Diagram

7-Way Trailer Diagram

Note: To ensure that your trailer connector is wired properly, we recommend using a circuit tester to match pins by function. Because wire colors can vary, they are not as reliable for determining functions. And improperly connected wiring can cause damage to electric components.

Mounting Your Trailer Wiring Harness

Often the 4-pole trailer connector will remain in the trunk or cargo area of a car or SUV when not in use. This helps to extend the life of the connector by protecting it from the elements and accidental damage. When it is needed for towing, simply pull the connector out and shut the trunk or rear door. The rubber weather strip that provides a door seal keeps the wire from getting pinched. If the trailer connector needs to be mounted under the vehicle, we offer many different mounting brackets that will help to protect the connector and keep it from dangling beneath the vehicle.

Trailer Wiring Adapters

Trailer Wiring Adapter Fitguide

The T-One connectors and hardwire kits all use a 4-pole trailer connector. This connector is most common among the smaller utility trailers and can easily be adapted to match the larger 5-pole, 6-pole and 7-pole styles. Using an adapter lets you avoid having to splice into the vehicle's wiring system. Adapters will plug into the flat 4-pole connector and have wire leads to provide additional functions such as powering trailer brakes, power lead for utility lights, reverse, or auxiliary power for a winch or tools. If your vehicle or trailer is equipped with something other than a 4-way plug, such as the larger 7-way round plug, you can use our adapter fitguide to find the one that is right for your vehicle and trailer.

Troubleshoot Your Trailer Wiring

Troubleshoot modulite wiring

If you have a Modulite (powered converter), Converter, or T-One connector that is not working properly, you need to use a circuit tester to determine the source of the problem.

Converter Shorting Out

When too many amps are drawn through the converter box, it can be shorted out. The possible causes are:

Weak Ground

Video showing how to wire the ground

If you find some, but not all, lighting functions work properly you may have a ground problem. In this situation a weak ground is just strong enough to provide some lighting functions but not all. When the taillights and brake lights are used at the same time, it creates the maximum amp load of the lights on the trailer. If a ground problem exists, it will show at this point. The places to check grounds are as follows:

NOTE: If you purchased your wiring harness from and none of these fix your problem please feel free to contact us so our product experts, and installers can determine possible remedies or warranty coverage.

How to wire your car or truck to pull a trailer

Trailer Wiring Options

By law trailers are required to have at least running lights, turn signals, and brake lights. To provide the power and a connection for these functions, the tow vehicle's electrical system needs to be tapped into. There are two options available for connecting to your vehicle's electrical system, a plug in style T-One connector or a custom selected hardwire kit.

T-One Connector

The easiest way to make this connection is with the use of a T-One Connector, which comes with OEM style connections that simply plug into your vehicle's existing wiring harness, typically near the rear of the vehicle or by the tail lights. Sometimes the vehicle manufacturer will run the wires to an easily accessible plug underneath the vehicle or behind the paneling in the back cargo area. T-Ones come pre-wired with a 4-way flat trailer connection and can be expanded to 5-way, 6-way, or 7-way trailer connections through the use of a wiring adapter.

Custom Hardwire Kit

Scotch Lock Illustration

If a T-One is not available, a connection can still be easily made by using one of our custom selected hardwiring kits. We offer kits with all the pieces you will need to simply tap into the existing wires on your vehicle. This may sound difficult, but quick splices make installing the wiring harness quick and easy. A quick splice has two grooves in it; one groove is for the vehicle wire, and the other groove is for the wire on hardwire kit. Once both wires are in the grooves, you simply press down on the top of the quick splice. This forces a metal piece into both wires, connecting the circuit and eliminating any need for cutting or splicing. To hardwire the tow vehicle for a trailer connector you need to locate the proper wires. To help in this task you can check the vehicle's owner manual or use a circuit tester. The circuit tester is used to make sure the correct wires on the hardwire kit are connected to the matching wires on the vehicle; it helps determine which wire performs which function. The easiest place to tap into the vehicle's wiring system is behind the tail lights. By turning on the left turn signal, a circuit tester can be used to test the different wires behind the driver's side tail light. When the circuit tester lights up, you know that wire carries the left turn function. A quick splice slid through the yellow wire on the trailer connector and around the just found vehicle wire will clamp down to provide a secure connection.

The three types of Hardwire Kits are:

  1. Standard 4-Pole Wiring Harness - For use with vehicles that have adequate power and standard wiring system, these simply connect into existing wires on the vehicle and have a 4-pole flat connector to attach a trailer.
  2. Converter - For use with vehicles that have separate turn and brake light wires. Some vehicles send only one signal per wire, creating what is called a 3-wire system: one wire for the left turn, one wire for the right turn, and one wire for the brake signal (common on vehicles with amber turn signals). A converter will reduce it to a standard 2-wire system needed for wiring a trailer. There are still additional wires for the running lights and for the ground. Any vehicle with amber turn signals will need a converter. However, there are some vehicles with all-red tail lights that can also require a converter. A wiring harness with a converter has a black box built in it. Five wires go into the box, and only 4 come out. The converter transfers the brake signal on the vehicle into the left and right turn signals for the trailer wiring system.
  3. Modulite or Powered Converter - Used with vehicles that do not provide enough electrical power to handle the additional strain of powering trailer lights, the Modulite or powered system draws power directly from the battery but still connects to the vehicle's wiring system to determine when to power the lights on the trailer. If there are too many lights on the trailer for the vehicle's electrical system to provide adequate power, use a modulite or powered converter. A modulite installs the same way as a standard converter except an extra wire must be run to the battery. Instead of drawing power from the vehicle wiring system, a modulite draws power directly from the vehicle battery. This is safer because the extra amps to power the trailer are no longer going through the expensive electrical components of the vehicle. More vehicles are using thinner gauge wire and require a modulite, regardless of how many lights are on the trailer, simply to protect their wiring system.

Wire Color by Vehicle Manufacturer

Dual Purpose Bulb System
Wire FunctionWire ColorGMCFordChryslerJeepToyotaHondaMazda
Right Turn & Brake LightsGreenGreenOrange w/ Blue StripeBrownBrownGreen w/ Yellow StripeGreen w/ Yellow StripeGreen w/ Yellow Stripe
Left Turn & Brake LightsYellowYellowLt Green Orange StripeDk GreenGrey w/ Black StripeGreen w/ Black StripeGreen w/ Blue StripeBlack Stripe
Tail LightsBrownBrownBrownBlack w/ Yellow Stripe or BlackBlueRed w/ GreenRed w/ Black StripeGreen or Black Stripe
GroundWhiteBlackBlack or GreyBlackBlack & BlackBlack or WhiteBlackBlack
Single Purpose Bulb System
Brake LightsUse ConverterPink or Lt BlueRed w/ Green StripeWhiteBlue w/ Black StripeGreen w/ Red or White StripeGreen w/ White StripeGreen or Green w/ Red Stripe
Backup LightsRedLt GreenBlack w/ PinkVioletBrown---
Electric Trailer BrakesConnect To Blue Wire From Brake Controller

Vehicle manufacturers have intermittently changed wiring colors over the years.

It is recommended that a circuit tester be used on the tow vehicle's wiring harness to verify that the correct wire has been located for the proper function.

Questions and Comments about this Article

Mark F.

I bought an 7 way trailer end with a junction box to retire my trailer. I am trying to have all lights on separate wires side markers and rear lights so I have 7 brown ends to put on stud in junction box. Don’t know If I can get them all on there. Could I put the 4 side markers on the black stud ? Or will the side markers be on all the time ? Or maybe the red ? 103359

Reply from Jon G.

I would limit the wire connections for your marker lights to 2. Normally trailers will have 2 running/marker light wires that run down both sides of the trailer and all of the running/marker lights are simply tied into them. Since you have 7 brown wires that need terminal connections I think you're hurting more than helping your cause. Most junction boxes have the terminals labeled so I'd try to stick to those labels to make all of your connections easier. 75807


I have a 2004 f250 super duty with a rugby flatbed. The wiring harness from the flatbed runs up to the truck side oem trailer harness. Most of the wires are double colored or striped which connect to the single colored flatbed harness wires. Not sure what all the wires are for exactly. Installing a new trailer plug directly to the truck side wires, I noticed that I have 2 blue wires that were connected to the harness. since I am splicing my 7 way plug directly to the truck side wires, would I run both of the blue wires to the correct plug connection? (blue wires are for electric brakes) basically there were 8 wires connected to the oem harness 2 of which were blue. 103324

Reply from Jon G.

You can either take apart the current connector on your 2004 Ford F-250 and then rewire the new plug using the same locations, or you're going to have to test each wire for it's function and then wire accordingly. If I had to guess I would think that the blue wires are maybe for your 12V power and one of them tees off to your truck bed but I could be wrong. Even though there are typical wire colors it doesn't necessarily mean that those wires colors actually carry a certain function - that's why it's always best practice to test for function. 75790

Reply from Mike

@JonG after doing just that the blue wires were for the brakes. I connected the 2 blue from the truck and spliced into the new trailer blue accordingly. After connecting all my truck side wires directly to the new plug, I saw that there are 4 extra wires which are striped; Orange/Blue, Green/Orange, Black/Pink and I believe Green/Pink (which was not used therefore I taped it up). I am now wondering if these 4 striped wires are what "would be" the wiring for a 4 way flat..?? Any idea what those striped wires are for? The flat bed harness consists of 6 wires which are Blue, Black/White, Brown, Yellow, Green, White. I now know what all these wires are for but I'm not sure what the truck side wires they are connected to are for. Blue is reverse connected to Black/Pink, Black/White is power but spliced into Brown and connected to Truck side Brown, Yellow is Right turn connected to Orange/Blue, Green is Left turn, connected to Green/Orange, and White is ground connected to Black and grounded to the frame. Photos would help I'm sure. Any idea of what exactly the truck side wires are for? Especially the one that is not used and taped. Thank you VERY much for the response! 75800

Reply from Jon G.

@Mike Those wires very well could be the wiring that was meant for a 4-Way wiring harness for trailer lighting. As long as your 7-Way has all of the functions active then I wouldn't worry about connecting any other wires - just make sure that they have been protected if anything is loose. If you are still missing some functions of your 7-Way then you can use the diagram from this helpful article to make sure you connect everything to the standard pin locations so that they match with any given trailer 7-Way. 75806

Eric R.

i have a 2000 model motorhome with amber lights, with a 6 pin plug and i need to wire a 3 to 2 converter to use the tow light kit. Can i wire that so ii still have the 6 pin and a 4 pin to choose from so if if i pull something with brakes i still have that option? Thanks 103323

Reply from Jon G.

If the 6-Way on your motorhome has the turn signals separated out from the stop signal then you'll want the converter there all the time anyways because trailers use a combined lighting system as well. You can use the Hopkins # HM48847 or the Roadmaster # RM-732 . 75789

Reply from Eric R.

@JonG a 4 pin flat won't operate a braking system will it? If so why have they steadily made vehicles with higher pins and blades as the years progressed? 75794

Reply from Jon G.

@EricR Fair point, I guess I should have asked what components you're using first. I was thinking you wanted the 6-Way for flat towing and then the 4-Way to tow a trailer. If this is the case then you should be okay but that kind of depends on what braking system you'll be using for your towed vehicle. If instead you're wanting to tow a trailer with brakes then you should probably upgrade your 6-Way to a 7-Way. You'll need to figure out what functions your 6-Way has so that you know what you need to add for the 7-Way. 75796

Chuck E.

I just bought a 2021 Kia Telluride and as part of the sell dealer installed a tow package. Problem they installed the 4 way plug and I need the 7 way system. Dealer said they would pay for the up grade but now they are starting to back track after I guess checking some prices. What's the easy and less expensive why this problem can be fixed. I'm pretty sure my boat trailer has to have power with the back up lights or the brakes lock up and you can't reverse the trailer. Any help and advice??? 103225

Reply from Jon G.

If you already have the 4-Way installed then you can use the Universal Wiring Kit # ETBC7 to give yourself a fully functioning 7-Way (and 4-Way). The only problem is that this will need to be spliced into your OEM wiring so if you're not comfortable doing that on your brand new vehicle then you might want the dealership to do the installation anyways (or at least a reputable shop). As of right now we don't have any kits that plug into a port or existing plug on your Telluride and give you all of the functions of a 7-Way unfortunately. 75735


Can you replace the inners of a Bulldog H85 boat trailer swivel wheel jack as this one the handle fell off and I can’t get into seeing how it goes back together .. I managed to get it apart down to the housing that holds the handle but can’t get inside of that as it’s welded together .. Please help if there’s something I can fix 101953

Reply from Jon G.

I wasn't able to find anything about a Bulldog H85 trailer jack but if you send me some pictures I can see if we might have something similar. Really though if the entire outside of the jack is welded together then I doubt there are replacement parts for the inside of the jack. 75170

David S.

I have a 2009 Class A motorhome on a Ford Chassis. There is a harness for the lighting no problem but there is also a two wire harness with a blue wire which I assume is the trailer brakes and a white wire. No continuity to ground, so what is the white wire for? 101893

Reply from Jon G.

If that white wire isn't a ground wire then the only other 2 functions it could be is the reverse or 12V power function. You can try testing the reverse function but for 12V power you might need to add a fuse or make a connection to your battery to make it active. 75144

Alvin E.

I have a 2004 Honda odyssey van with a harness and converter that converts 5 wire to 4 wire. when I apply my vehicle brake I get full voltage to the yellow / left signal and only half voltage from green/ right signal. When my trailer is hooked up I get very faint flashing on right signal and brake light is dimmer on right side also.. Running lights seem to be fine. Do you think I have a vehicle wiring problem , converter problem or both. My relays on the van test good at the harness plug at the rear of the van. My lights on the van operate fine with, or without the trailer hooked up . The trailer.wiring is correct and has been tested to be in excellent condition. Lights work perfect when used on other vehicles. Can you help me solve this issue? The Harness has worked fine for the last five years. Do you think I have developed a bad ground, or a faulty relay somewhere else on the vehicle that is causing this voltage drop on my right side brake and signal. What voltage I have on the right side is exactly halve what I get on the left. 101692

Reply from Jon G.

I would recheck the ground for the wiring on your Odyssey. If you have a wiring kit like the T-One # 118336 that plugs right in to a plug on your van then it is probably the converter. Sometimes something weird can happen that will short out the box. What I would do is test the pin on your van plug that is for the right turn signal. You can also test the wires going into the converter and the green wire coming out of the converter to see what is happening with your voltage. 75049


I bought an old travel trailer frame converted to a utility trailer a few days ago. It has dual axles with electric brakes and for some reason has a 12 volt battery still hooked up at the tongue that I believe may be hooked up to the electric brakes. I drive a 2007 Toyota Tundra . When I hooked it up to tow it my check engine lights , traction lights and 4 lo lights came on . It has a 7 way plug as does the trailer. I did not have a brake controller installed so thought that this was the problem so I ordered one from and installed it yesterday. Now when I plug it in the 4 lo light comes on. Any idea where the problem may be ? What is the battery for on the trailer ? thanks-- 99287

Reply from Jon G.

The battery on the trailer is actually a good thing. That is a breakaway battery and it is designed to activate the brakes in the event that your trailer comes uncoupled from your Tundra. There should be a pin on it that you want to loop around your safety chain loops. Here is an article you can check out for more info. From what I could find online it looks like the 4lo light might mean that your brake stroke sensor is bad. I'd get it checked out by a trusted mechanic just to be on the safe side of things. 73820

Greg W.

I have a 2007 ford super-duty with a new cm flat bed, pulling stock trailer, lights work, brakes work but the truck throws check trailer signal in dash and alarm beep, very annoying 99141

Reply from Jon G.

Check the 7-Way on your Super Duty as well as your trailer for any debris or corrosion and clean it out accordingly. If it happens at random then that sounds like some debris might be getting into the connection and causing this to happen. If those look good then the next place to check would be your grounds. Double check to make sure they are securely connected to a clean, bare-metal surface. 73725


In over my head, probably, but wired a 7-pin to a 6-pole flat and nothing is really working. Green, black, and white wires for side lights and tail lights with a red on the left tail light and a brown on the right tail light. Thought I could just connect color to color from the pigtail, but . . . I left the black (what I thought was the 12v wire) disconnected. Do I need to test the vehicle side or ??? Very confused and planned to be on the road tomorrow afternoon! This is for a 2005 Viking Saga pop up camper. 99094

Reply from Jon G.

You want to connect the wires to the pins according to function instead of color. The colors that we show are common but there isn't anything stating that those specific wire colors HAVE to be used. If you match up your wires and pins by function then you should be good to go! 73689

Warren F.

Question- I bought an old horse trailer and the previous owner converted it to a 7 pin plug (it has 6 wires). My colors don't seem to match with what you have listed above. Is that a common issue? My black is hot, white is ground, brown is running lights but, red wire controls the right turn signal while blue controls the left. Green it seems is for the brakes but I haven't gotten them to work just yet. 99085

Reply from Jon G.

The wire colors that we list are common wire colors used but there isn't any kind of law that requires these colors. Most of the time when someone has switched out wiring (like what you've found on your trailer) the colors don't typically match so you want to wire everything up by function instead of color. Then just make sure that your tow vehicle 7-Way matches those pins and you'll be good to go! 73688

Ron M.

Had difficulty wiring a trailer from a 4 pin to 7 pin so I could use the brakes on the trailer but it ultimately needed to go back to the 4 pin. But even when using the factory installed 4 pin and 7 pin combo on my 2013 F150, the running lights do not come on. Even when using a different trailer that I know is wired correctly. I think I checked all the fuses but appear good. Suggestions on how to get my running lights back? 98997

Reply from Jon G.

Check the fuse in position 67 in the fuse panel under your hood. If that looks good then your next step is to test the running light pins on your F-150 to ensure that they are actually sending out that signal. You can check out the attached articles to see where those pins would be located on your connectors. If you aren't seeing power on those pins when you turn your headlights on then this means there is something wrong with your OEM wiring. 73643

Mike L.

is there a way to go from the towing vehicle that has brake & Rt turn on one wire and Brake & Lt turn on another wire and Tail lights on another wire to a vehicle that has separate bulb for brakes, turn signals and tail lights. 98742

Reply from Jon G.

Are you looking to tow a trailer with 2 different vehicles, or are you talking about towing a vehicle with another vehicle? Both are possible but the wiring needed will be different. If you can let me know which method you're needing to do as well as the year.make/models of your vehicles I can help you out. 73522

Reply from Mike L.

@JonG My motorhome has the combined type of lights. I will be towing a 74 VW that has a wire going to each function, Lt turn, Rt turn, Brake and tail lights. When I have tried to wire direct to the VWs blubs when you use the turn signal both lights flash. 73536

Reply from Jon G.

@MikeL Ah, I see. Since your brake lights are separated out from your turn lights we'll need to look into using a converter box to split that signal, but even with a standard lighting kit your turn signals shouldn't be coming on at the same time. If you can let me know what model VW you have and what wiring you're currently trying to install I can see what parts we have that will work. Would you be opposed to a light and bulb system like the Roadmaster Kit # RM-155 ? 73598

Gregory S.

I have an RV on a Chevy 4500 chassis with a factory 7-pin trailer connector. The lights on my towed (Jeep Wrangler) vehicle do not work. Have verified a lack of power to 12-V pin on connector; jumping that temporarily makes everything work. What gauge wire and size fuse do I need to make a repair? 97978

Reply from Jon G.

Hmm, the 12V pin on your RV 7-Way shouldn't be a determining factor when it comes to the lights on your towed Jeep Wrangler operating correctly. Do the other pins on your RV 7-Way show the correct functions? What wiring kit are you using the power the lights on your Jeep, and what year is your Wrangler? We recommend using 10 gauge wire # 10-1-1 for the 12V power function. You'd want to have that running through a 40A circuit breaker like part # 9510 . 73007

Reply from Gregory S.

@JonG It's a 2011 Jeep Wrangler Unlimited 4dr with the dealer installed #82211156AB dealer wiring kit. I have a 7 pin tester with LEDs. I jumped a wire with a 5 amp fuse around the vehicle from the battery to the 1oclock pin, and the cable and all lights worked and tested good. Take it off and the tester shows lights but the Jeep does nothing. 73010

Reply from Jon G.

@GregoryS The 1 o'clock pin is the pin for 12V power and shouldn't be affecting your tail lights. I may have misunderstood but did you try running through the functions and testing the 7-Way on your RV only? If your RV isn't sending those signals to the 7-Way socket at the back then that would be the issue. 73127

Reply from Gregory S.

@JonG, Yes, I tested the RV 7 pin connector extensively with an led tester, another trailer, and a circuit tester. I am told some trailers need this. Towed vehicle & cable all work great on a 2019 Chevy Silverado. RV & Jeep lights work if I supply 12 volts to pin. 73131

Reply from Jon G.

@GregoryS I've heard of some of the newer trucks having sensitive electrical systems but this is the first time I've heard about this kind of problem with RV wiring. I would say do whatever you need to do so that your Jeep lights work. When we install wiring for the 12V power circuit we use 10 gauge wire # 10-1-1 . 73188

Reply from Gregory S.

@JonG I used 12 GA because that is what I could get in the time frame I had. The original factory wire looks like 16 Ga, same as the rest, so this is heavier. Thank you for looking into this. 73204


hooking up my four way wires from my truck to my led three wire ,which are black red an white coming from the truck the wires are brow and green and brown and yellow what wire go where? 97909

Reply from Jon G.

You're going to have to use a circuit tester to determine the functions of the wires coming from your truck. I wish there was a "set-in-stone" color code for wiring and what functions they carry but unfortunately there isn't. You'll want to use the connector diagrams in this article to make sure you have the correct functions matching up with the standard pin locations. 73006


2004 ram 2500, i have the 7 blade and 4 pin flat, i am only getting 12v back at my factory connection. And the 7 blade is new,checked all connections the whole way up to the TIPM. I have heard they go bad. Is there a way to fix it, or bypass it? 97876

Reply from Jon G.

If you want to bypass the OEM trailer wiring on your 2004 Dodge Ram 2500 then you'll want to install the Curt T-Connector # C55504 along with the Wiring Kit # ETBC7 . This gives you everything you need for fully functioning 4-Way/7-Way connections. Aside from bypassing all of the factory provisions the only other thing I know of is for you to check all of your fuse and relays that are related to trailer lights. 73005

Jay G.

I have a 2015 Coachmen Travel Trailer pulling with a 2017 F250. All trailer lights and brakes work when I get moving down the road, but if I drive through rain I get a message on my dash saying "Trailer Wiring Fault" then I have no trailer brakes, or worse, I will have trailer brakes intermittently. All lights on trailer still work. When the rig dries out, it all seems fine again. I thought it would be the trailer ground connection and I have cleaned and scratched it thoroughly and applied dielectric grease, but the condition seems to come back in wet driving conditions. Any ideas? 97482

Reply from Jon G.

Inspect all of your connections for your trailer brakes all the way from your tow vehicle through to the trailer brakes. Look for any places where there might be a break or maybe a damaged butt connector. Since this only happens during the rain you are getting water in that circuit somewhere and it's causing that circuit to do haywire. If you're using regular butt connectors for your wiring connections swap them out for heat shrink connectors # DW05745-10 which do a much better job at protecting the wiring. 72648

Joey K.

I basically would just like to ask a question. My son has a 2010 super duty f350 diesel dully. The trailer light switch is a factory 7 blade 4 flat plug. He can hook anything up on the round 7 blade connector and everything works properly. When he hooks his boat trailer to the 4 flat plug everything works except his running lights. He says he has checked all fuses and they were good. 2 of the blades on that plug are for right and left turn signals and they test hot. The other pins left on there is the running lights (no juice), and I’m assuming the last of the 4 is a ground. Problem has to be from the 4 plug towards the front of the truck. Can you give me an idea what may be going on? Thank You 97093

Reply from Jon G.

It could be a bad wiring connection or maybe some corrosion on that 4-Way. Does the 7-Way connection show the running/tail lights? It should be the pin in the 11 o'clock position. If it shows power then the 4-Way plug is bad and needs to be replaced, but if it doesn't show power then something is going on between the OEM wiring and that plug like loose or damaged wires. 72646


I don’t really have a comment, I’ve gotten a question. My factory plug 7 pin round and 4 pin rectangular all made together. My 7 pin works fine, it’s I plug my boat trailer lights into the oblong one and I have all working lights except taillights and running lights. We have checked the fuses supposedly and even put the whole new plug on it. What is could it be to make my running lights not work? 97091

Reply from Jon G.

Try checking the connections for those lights and be sure to look at the grounds as well and that they are securely connected to a clean, bare-metal surface. It would also help to test the 7-Way and 4-Way connectors on your tow vehicle to make sure that the running/tail light pins are actually putting out power because the issue could also be on your tow vehicle. 72645

Ken B.

Putting new 4 prong connector on Marathon trailer there are 5 wires 1 white,1 yellow,1 green,1 brown and a brown with yellow strip where do I hook that one 95798

Reply from Jon G.

Normally when there are 2 brown wires on a trailer-side 4-Way connector it's because they both carry the running/tail light function so you can run each wire down either side of your trailer to make it easier to tie-in your clearance lights. Just apply 12V power to the pin for the running light circuit (exposed pin closest to sleeved pin) to make sure that both brown wires get hot. Here is a link to our article about 4-Way wiring. You can use the 4-Way Flat picture to see which pin I'm talking about. 70603

Leonard M.

7000 lb axles, tandem, brakes wouldn't lock up. Tried two different chev trucks, both the same. Is there different magnet strengths? How do you know if your magnets are weak? Brakes where pulled, cleaned and set with a slight drag. They brake slightly but should lock up with your controller set to max 10. 95523

Reply from Jon G.

Were you driving when you tested the trailer brakes, or were you just parked and pressing the brake pedal on the trucks? Normally when we have someone with the problem that you are talking about it's because they have a proportional brake controller that senses the truck isn't moving so it hardly sends any power back to the brakes when the pedal is pressed. If the brakes aren't locking up and you're testing with the manual override then that's a different story and it sounds like you have some damaged wiring, possible corrosion in a connector, or a bad ground on the brake circuit. 70602


I have an 05 xterra. When running a trailer lights they all work except the left break light and the left turn signal. The left light works for the running lights. I've replaced the T-harness but still doesnt work. Which wire should I look to replace to get this to work? 94867

Reply from Chris R.

Have you tested the 4-Way on the Xterra for power to make sure that left brake/turn light circuit isn't getting power? It's possible that the issue is actually on the trailer. Test the 4-Way with a circuit tester to ensure you aren't getting power to that pin when activating the turn signal or brake light in the vehicle - if you ARE, then there's likely a weak ground connection on the trailer. Check the main harness ground as well as the ground for the tail light assembly itself, making sure they're still secured to a clean, bare metal surface. 70218

M. S.

I have a Tarnel Utility trailer that the wiring got pulled from the 7 way plug. The wires going into the plug are: Yellow, Red, Green, and Brown. The 7 way plug has no yellow position. I can't seem to find out where it would go. I'd appreciate any help. Thank you. 91908

Reply from Chris R.

The yellow wire is most likely for left turn/brake light signal. On a 7-Way this pin/circuit is at the 3 o'clock position when looking at the back of the connector. 68381

Nathan B.

I have an old jetski trailer that I converted to a flatbed and only my right turn signal and right brake light works and its grounded right but I have two other wires one for left turn and for right turn thats not connected would that be my problem. 86499

Reply from Chris R.

I'm not quite sure what you mean by the left and right turn wires not being connected. Are they just left loose on the flat bed? That would certainly be the issue if so - if you mean something different please let me know. 68380

Reply from Nathan B.

@ChrisR I found the problem it was my converter from a 5 prong to a 4 prong. So I cut that off and wired it straight into the truck. 68429

Reply from Chris R.

@NathanB Great! 69745

Will D.

I have a question...if you are running brakes and signals off the same pole then how do you wire it so they dont cancel each other out? I can do one or the other but when I try to do two, my hazards don't work like its shorting something out. I have tried connecting them at different points along the wire but always get the same result. Any tips would be greatly appreciated 86075

Reply from Chris R.

The same wire should be used all the way along the trailer - the circuits combine at the tow vehicle's harness. Are you installing brand new wiring on the trailer or simply repairing? 67925

Sean K.

My taillights were taken out by a hail storm. I need to replace them. My trailer has 4 wires .... taillight, ground, turn and brake. Is it possible to buy a 3 wire new light.? Twist the trailer side brake and turn together (the brighter, higher output circuits) and connect them together to the turn/brake wire of the new light? 84751

Reply from Chris R.

So you have a separate wire for turn and brake signals on your trailer? That's pretty unique. Unfortunately just tying those wires together before the new tail lights would work to properly illuminate them. Your best option is to actually install a converter like # RM-732 in-line to combine those circuits. 67701

Reply from Sean K.

@ChrisR So I finally did some more exploring and determined the following .... At the taillight my trailer (1991 Terry bumper pull 19') has 4 wires. White for ground, red for brake/turn, and 2 - green running light wires. Both running light wires attached to my old taillight, but it's only a single bulb taillight...... So I am unsure why there are 2 running light wires??? Taillight and license plate light ? Except there is no separate bulb for the license plate. Does anyone have a wiring diagram for this old of a trailer? 70510

Reply from Jon G.

@SeanK I think you're right about 1 of those wires being for the tail light and the other for the license plate light. With a trailer that old it's possible that someone else did some work on the trailer if that second green wire wasn't connected to anything. As long as you have your lights installed correctly and your license plate is illuminated you should be able to just cap off that second green wire. Typically when you see 2 wires for the running lights you find it up at the connector. This allows you to run 1 green wire down each side of your trailer to make it easier to connect clearance lights. 70600

Joel R.

I have a 2018 Thor Axis M25.3, and the 15amp fuse for the parkng lights keeps popping. I have a 7 pin trailer pin on it but I see nothing wrong with it. Now I saw a black cable grounded to chasis hanging but is was like 2 inches wraped around other wires and not going to anything. I replace the fuse turn my lights on it popped any idea since this is a new no one has messed with or no damage to the harness. 84465

Reply from Chris R.

It definitely sounds like something is shorting out to the frame. Even though it's a new harness, make extra sure that there's no exposed wiring making contact with bare metal. Also inspect the 7-Way on the trailer side for any corrosion that might be built up inside the pins, cleaning out as needed. Let me know what you find and we can go from there. 67383

Kevin S.

Boat trailer with led lights. One side got smashed so I bought a new set. I can't get the tail lights to work at all. Brake and turn work. I put the good old led tail light back on its side and it works 100%. Why am I not getting tail lights on the new set? Just turn and brake? 84446

Reply from Chris R.

Is the new set identical in terms of wiring? If the new assemblies ground through their mounting hardware (don't have a dedicated wire for ground), make sure they're attached to a completely clean, bare metal surface that's free of any debris or corrosion. A weak ground can often cause issues like this. Let me know what you find and we can keep troubleshooting if needed. 67382

Reply from Kevin S.

@ChrisR so the new led lights have a white ground. The old ones were internal to stud. I put the new white ground to the stud (also tried screwing to frame) and all but the tail lights work. The other two wires to the light were grn and brown and the leds were red and black. Red to grn , black to brown but no tail light. Switched them and had tail light but no turn or stop light. 67404

Reply from Chris R.

@KevinS So the fact that switching the wiring on the assembly let you have tail lights (but not turn/stop) makes me think the issue MIGHT actually be on the tow vehicle. Have you tested the 4-Way or 7-Way (whichever you have) on the tow vehicle to make sure you're getting power on the running lights pin when those lights are illuminated? 67700

Reply from Kevin S.

@ChrisR I did test the connector at the vehicle. It was fine. I was just about to start changing the wires out but my brother had another led light he wasn't using. I I put the original and my brothers on. Both work as they should. I have all my lights. I can only guess the wiring in the new led lights is bad. I'm returning them back as defective. I thought maybe because they came in with red and black leads and a white ground, I was doing something wrong. Thank you for your replies and thoughts!! 67708

Reply from Chris R.

@KevinS I'm really glad you were able to get it resolved but I'm sorry that the new lights were defective. Happy towing! 67924

Mike R.

I have a tow vehicle issue. 2012 f150. I had no power at connector/harness. I replaced fuses/relays and still no power. Was told it could be a computer issue. So with that I decided to hardwire to tailamps. Finding running lights and connecting was no problem. We have lights on the trailer now. Good right? Not yet. Found what I thought was the turn signal wire(left) and as soon as I connect the trailer line(yellow wire) I get a rapid blink as if a lamp is out. Everything blinks rapidly so that’s not the case. I thought maybe something wrong with the trailer so had another vehicle hook issues. I am at a loss of why it would send a signal like a lamp is out. Any help? 81947

Reply from Chris R.

It's possible that the turn signal circuit on the truck isn't strong enough to power both the truck's lights and those on the trailer, so less than what is needed is going to the truck and thus triggering the "lamp-out" rapid blinking. What type of harness did you install? Did it feature a powered module that gets wired up to the battery? 67139

Reply from Mike R.

@ChrisR I never installed one. Came from the dealer with a tow package when I bought it years ago. Everything worked fine up until this year. So I’m not sure. 67162

Reply from Chris R.

@MikeR I apologize, I thought you said you hardwired in a new harness to the tail lamp circuits. Is that not correct? 67381

Henry R.

Dear Sir, My situation is my running and tail lights work but turn and break lights do not. Tow vehicle is a 2016 Sorento and trailer is a 1973 Apache pop-up camper. Connects with flat -4. Using a flat-4 tester all to vehicle functions work. When connected all lights light (running-tail), but no break or turn. When Left turn signal engaged tow vehicle left turn signal does not work but right tow vehicle light does. I have run new trailer wiring and lights from a harbor freight kit. Grounding on the 73 Apache is from the tow vehicle (as outlined in the camper manual), NOT on the camper frame. Thanks for any advice 81664

Reply from Chris R.

I believe you said that all the functions tested correctly on the Sorento's 4-Way connector. If that's correct then we know the issue is somewhere on the trailer side. I would check the grounds on the individual trailer light assemblies themselves. They'll either use a dedicated ground wire or simply ground through their mounting hardware - in either case make sure they're attached to a clean, bare piece of metal on the trailer. Let me know if this doesn't help and we'll keep going. 67138

Colin C.

I have a 2020 Dodge Ram 2500 and a trailer that I would like to have a dedicated battery to run, lights, fan, water pump and electronics. My understanding is that my 7 pin 12V from the truck will not charge the trailer battery only maintain it, although I am getting 14.2 V on a Volt Meter at the pin. I plan to plug the trailer in over night to shore power. So I will have a 12V source to my trailer battery from the 7 pin and a converted 12V srouce from shore power via a charger. Do i need to isolate these two circuits from each other? If I have the 7 pin disconnected and the battery has power then thats going to be a Hot pin coming off the trailer? If I have the 7 pin connected but the truck off is my starter battery isolated thru my truck or is it possible I will continue to draw off the starter battery? 80528

Reply from Chris R.

That charge line can definitely continue to draw power from the truck's battery if you leave the trailer plugged in (and the truck is turned off). I recommend adding an isolator like # TR118665 inline with the power wire going back to the 7-Way. 66335

Bridget K.

My boat trailer lights seem to work fine, however after running down the road for 45 minutes or so - they will turn turn off. Next day, same thing they will work fine, but then after a period of time turn off again. I have a basic 4-way flat connector. Side marker lights converted to LED, clearance lights (If I can call them that) on center frame of trailer converted to LED. Turn and brake are original bulbs. I've ensured that trailer ground is clean and connections to turn/brake are clean. I have a multimeter arriving today so that I can start to sort this out. Any suggestions on how to diagnose the issue? 78021

Reply from Chris R.

That is a bit strange. And you aren't doing anything to reset the circuits between each trip (replacing a fuse, etc) - they simply work when heading out on the road again (for 45 minutes)? This sounds like a loose connection somewhere. A couple of things you can look at. I would first just make sure that you're able to get a clean, secure attachment between the tow vehicle and trailer 4-Way connectors. Make sure there isn't any bent pins that need to be straightened or corrosion/debris stuck inside of them that needs to be cleaned out. Even though you already did this, I would also check the grounds one more time. If your boat trailer is aluminum, I would run a dedicated wire all the way up to the main harness ground. 63503

William R.

I have a 2018 Silverado 1500 I installed a tekonsha p3 brake controller and wired it to the adapter that came with the vehicle. When I drive and manually engage the brake controller it says output shortage and when I use the pedal it says overload I can’t figure out the problem. The breaks start going as I ease it on then once I engage them harder these warnings come up 77145

Reply from Chris R.

It sounds like there's a short somewhere on the brake output (blue) wire coming from the brake controller. Make sure that particular wire has a good connection and inspect the 7-Way at your Silverado's bumper for any rust or corrosion that might be built up inside the pins, cleaning out as needed. Let me know what you find and we can keep troubleshooting if needed. 62701

Reply from Larry L.

@WilliamR Rewiring/rebuilding 1978 Wilderness. after wiring brake system, pulled breakaway cable to check for action. finished wiring and noticed brake controller going red when activated. Started using ohmmeter checking for shorts, grounds. Opened 7 way connection box and started checking brake cables. Noticed that blue cable was drawing 8 ohms resistance. replaced breakaway unit, solved problem. Breakaway unit was rusted and evidently rust was conducting voltage.. 63102

James G.

I have a alum trailer I replaced to rear lights with LEDs now it seems ever yr.1/2 the wires corrode and I need to rewire the trailer. What would cause this and is there a fix. Thank you 76932

Reply from Chris R.

I'm really not sure. Do the lights themselves seem to work normally through the season? Are they corroding at their connection to the light assemblies or somewhere else along the trailer? Using heat shrink butt connectors like # DW05744-10 at your connection points will help to prevent rust and exposure over time. 62700

Reply from James G.

@ChrisR the wires themselves corrode they get all white powder on them and it eats away the copper wires. Then everything goes dead. This is the third time it happened. 62704

Reply from Chris R.

@JamesG Thanks for the info - the only thing I can think of to try to prevent this from happening again is to switch to heavier gauge wiring. Do you know what size wire you're currently using? 62871

Reply from James G.

@ChrisR I was using the wire set up they sell at tractor supply it kind It is thin. I am now in the process of replacing all the wires again but now I am using a junction box with a extinction cord wire thinking it's about 16 gauge. 62877

Reply from Chris R.

@JamesG Great - hopefully this resolves the issue and you don't have to deal with it again! 63046

Reply from Jared W.

@JamesG Use Dielectric Grease on ALL your connections, switch your butt connectors and ring terminals to ones that are the waterproof heat shrink kind and squirt the dielectric grease inside of the connector prior to crimping it and then heatshrink the connector. Don’t be afraid to hold direct flame to the heatshrink. M Keep the flame moving and ensure that it fully shrinks all the way around. It’ll force out excess dielectric grease and you’ll have a waterproof connector typically good for 5 years or so. Use corrosion-x in the red can and spray all your terminals, wire ends, etc. throughout the year every month or two. I spray the entire engine inside the cowling of my Yamaha and it looks brand new. 66252

Jeff N.

Have a 2015 Toyota Sienna XLE with no trailer tow wiring. Installed a flat 4, then had to add a flat 4 to 7 pin adapter to use with a rental. Just purchased a popup (2017 Palomino T12 STS) with electric brakes, and dealer sold me a Curt Echo wireless brake controller (but did not do the full wiring required for brakes). Question is, on the Hopkins 4 to 7 adapter, the black wire goes to 12V power, the white wire goes to ground. That leaves the blue (brakes) and purple (auxiliary) wires. Blue is for brakes, but since this is a wireless controller, do I use the blue to tap into the cold side of the tow vehicle's brake pedal switch? Appreciate the help. 76367

Reply from Chris R.

The beauty of the Curt Echo # C51180 comes out in times like this. On the Hopkins Adapter you recently purchased, the black 12V wire you mentioned (along with the white ground wire) are the only wires you need to actually connect. The blue brake output wire - which is used for most other traditional controllers, isn't needed. It and the remaining wires can just be capped off. The Echo needs only the 12V and signal light circuits to operate, as it uses its accelerometer to send power back to the brakes based on deceleration. 62332


I have a 2018 travel trailer, which pulled perfectly for 2000 miles. I recently hooked it up to move it and didnt have my backup camera after turning on the lights in the truck. The 20A fuse in the truck blew. Ive checked the truck and I have good ground at the plug in and clean 12V. Ive replaced the 20A in the truck and all works fine when not connected to trailer On the trailer, when I put the positive probe of my circuit tester into the tail/running light slot of the plug, and then touch the negative probe to the ground wire in the junction box, I get a constant circuit beep. For that matter, if I touch the negative probe to the box itself I get a constant circuit beep. Should I see a circuit between the slot in the plug for tail/running lights and ground? All bulbs have been removed to check them for damage, so no bulbs are currently in their sockets around the TT. I wanted to bypass the 7 way plug and pigtail to make sure the sealed plug itself didnt have a ground problem, so I wired a jumper from the truck tail/running light to the tail/running light slot in the plug, and ran a ground from the truck plug ground directly to the battery ground. The lights worked fine. When I moved the ground wire from the battery ground to the frame ground, the 20A fried. Seems I have an energized frame, right? The tail/running light wire has grounded somewhere, so its energizing the frame when connected to 12V. Is this why I get a constant circuit beep when I connect the probes to the tail/running light slot and the ground slot in the trailer 7 way plug? If my assumptions are correct which is likely a longshot, are there any tricks to help me find where the tail/running light wire may have grounded? My TT is underskirted, so the wires all disappear and are out of sight. Before I start digging, Im hopeful theres some way to narrow down the location. Thank you! 76028

Reply from Chris R.

I definitely think you've at least determined the cause of your issue. There's likely an exposed section of the running lights circuit wire that's touching bare metal somewhere along its length. I REALLY wish I had an easier solution for you, but the only real way to track this down will be to try and dig up the wiring and inspect it along the trailer, looking for any damaged portions that need to be replaced. The only alternative would be to simply cut that wire off from power and run a new wire for this circuit. 62131

Reply from Justin

@ChrisR Thank you Chris, I appreciate your time and expertise. I was hoping the answer would be different, or you could point me to the magic eTrailer short detection magic box. At this point, I'd pay quite a bit for one of those! Thanks again. 62188

Reply from Chris R.

@Justin We JUST ran out of our magic short detection boxes......joking aside when I invent one I'll be sure to send you a share of the profits. I completely understand what you're saying though. I really wish I could have given you a better solution - it really might be easier to actually run a new wire than try and dig up where the short is. 62331

Jim R.

I hav a 7 way hooked from truck 2 gooseneck..everything works fine..i need a battery 2 run a motorized jack i hook a battery positive 2the hot wire in 7way box.neg.goes to 7way box neg terminal ...jack works perfect .but throws a code in brake controller ..explain this please 75753

Reply from Chris R.

I'm honestly not sure why running a power wire from the 12v circuit on the 7-Way (and then to your battery) would trigger any error codes on the brake controller, as this circuit should be totally separate from it. Is this a factory brake controller? What kind of error code is it giving you? 61861

Ken S.

i have a 2004 chevy silverado 1500 my trailer has power to my left turn signal all the time when i turn the flasher on it flashes as it should when i test the plug with a test light it does not light the light but with a volt meter i get 12 volts some times after you turn on the right signal the left will start working properly again then after using the left signal it is back to having power at the plug again my truck lights all work properly trailer lights work fine on my other silverado was wondering if it may be the converter ? was told it could be the flasher module 75749

Reply from Chris R.

It could indeed be a bad converter - you could try testing the wiring right before the converter and then right after to see if there's a discrepancy. Otherwise I would visually inspect the truck's 7-Way for any corrosion that might be built up inside the pins, cleaning out as needed. Rust build up can lead to a short, which can cause issues like you're dealing with. Let me know what you find and we can go from there. 61860

Joe F.

2019_chev y Silverado 3500 with no current at auxiliary blade in connector. Checked fuse and it is good. Any suggestions? 75719

Reply from Chris R.

If the fuse is good and you still aren't getting any power on that circuit, make sure you're testing the pin with the truck running. Some models only send power back when the ignition is on. If that isn't it, then you're only option is to physically inspect the auxiliary wire going back from the Silverado's 7-Way if possible. If not, you can always just bypass it and run you're own by using 10 gauge wire like # 10-1-1 from the 7-Way to your battery via a breaker like # 9510 . 61859


My RV is on a freight liner xc chassis, page 6 wiring diagrams says they pre wired a connector to the rear of the vehicle. A where is it, B do they make a prewired outlet that plugs into the XC harness?Do they have harness that we can use to add an outlet C would you have one? 74200

Reply from Chris R.

Factory connectors are usually hidden behind the rear bumper - you'll likely just have to dig around underneath to pull it down. Can you tell me what model year the Freightliner chassis is? 60366


Which wires get connected to what at taillight? I have two screws to connect. Brown wire and the light would go together to have power. Turn signal wire would also be on this connection? Searched and searched with no answers. Should of taken a picture before I took it apart.Thanks! 71757

Reply from Chris R.

Can you tell me what model tail light assembly you are installing? If the light is serving as both the tail light for running lights and for turn and brake signals, then the turn/brake signal wire would go to it as well. If you can tell me what model light you have though I should be able to give you a more specific answer. 58781

Justin B.

Hey there,I have a 2014 3500 that I use on a regular basis to pull materials for work. I was curious if you knew the amperage or the voltage that comes out of the trailer plug on the back of the truck?The reason I ask, besides not finding any info anywhere, is that we want to install new lights or a string of lights inside the trailer, and wanted to make sure we didnt short it out.Any info would be greatful!Thanks!J 64378

Reply from Jacob H.

I would recommend replacing all of your lights with LEDs and whatever lights you decide to add make sure they are LEDs also. If the lights look like they are dim or flickering you can add a battery to the trailer for the extra lights inside and run a charge line from the 7 pole plug to the positive side of the battery that way it maintains a charge. 54737

Clif P.

I have a 14,000 pound tandem trailer just put new drums and new electric brakes on new wire harness to battery release and vehicle has power to wheels but has no extensive stopping power what do you think could cause The wheels to stop when we left trailer off of ground but on the ground brakes do not have enough power to stop the wheels 64201

Reply from Jacob H.

It sounds like you need to adjust your brakes. If the breaks are not adjusted properly you have a very weak amount of break pressure being applied to the trailer. We have the tool needed to adjust them and I will provide a link to find it. 54486



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