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Trailer Wiring Junction Box

Trailer Wiring Junction Box

Item # 38656
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This Spectro trailer wiring junction box provides a fast, easy way to connect the wires from the trailer connector to the wiring for either a 6-way or 7-way connector. Makes replacing your trailer's connector simple. 1-636-306-4830 to order Spectro accessories and parts part number 38656 or order online at Free expert support on all Spectro products. Guaranteed Lowest Price and Fastest Shipping for Trailer Wiring Junction Box. Accessories and Parts reviews from real customers.
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Spectro Accessories and Parts - 38656

  • Trailer Wiring
  • Junction Box
  • Spectro

This Spectro trailer wiring junction box provides a fast, easy way to connect the wires from the trailer connector to the wiring for either a 6-way or 7-way connector. Makes replacing your trailer's connector simple.


  • 7-Terminal junction box lets you easily connect your trailer wiring to a 6-way or 7-way trailer connector (sold separately)
  • Weatherproof, heavy-duty plastic protects wires and terminals from the elements
  • Mounting hardware included
  • Ring terminals (44-5310A) sold separately


  • Box dimensions with lid: 7" long x 3-1/4" wide x 2-3/4" tall
    • Overall length (with mounting flanges): 8"
  • Distance between mounting holes (on center): 7-3/8"
  • Mounting flange dimensions: 3/4" wide x 1/4" thick
  • Outer diameter of terminals: 3/16"

9709 Spectro Trailer Wiring Junction Box

Video of Trailer Wiring Junction Box

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Spectro Trailer Wiring Junction Box Installation

Today were going to install part number 38656. This is a trailer wiring junction box. First thing were going to do is find the location for our junction box. Were going to go ahead and install on the inside edge of the tongue. Well go ahead and hold it up to the tongue and then well go ahead and use a drill to mark it for our holes. We have our holes marked, well go ahead and remove the box, and then go ahead and drill out our hole.

Now well go ahead install our hardware and install our box. Now were going to use a quarter inch hardware to install the box to the frame. This hardware does not come with the box. With our box installed, we can go ahead and start getting our wiring ready. Well go ahead and cut our wires to the length of what we need and then well take our excessive length from our gray cable and use the white wire for our ground lead.

Were going to take the white wire, well add a couple of ring terminals, and well go ahead and connect it to the post labeled white and ground. Well also change out one of solid grommets for a hollow ground. With our new grommet installed, well go ahead and fish our wire through, and attach it to the box, and then were going to use a self-tapping screw to attach it to the frame. Now well go ahead and get the rest of our break cable ready, the gray cable will be for our electric brakes. Well cut back the gray sheath to expose our two wires.

Our white wire will go to ground, our black wire well go ahead and post to label blue, blue is only the function for brakes. Well go ahead add some ring terminals to it, then temporally put them into position. Now well go ahead and hook up our wires for our trailer lighting, well also go ahead and run it through the grommet and then go ahead and install our ring terminals. Now the brown wire on our trailer will be even running light circuit that will go to the post labeled brown, it will also say taillights on there. The green wire will be our right turn signal, well go ahead and connect that wire to a post labeled green, and it will say right turn.

The yellow wire well be our left turn signal and that will be connected to post labeled yellow and left turn. Now these wires have been loosely installed. Next well go ahead and wire our trailer connector, this is going to be a seven molded trailer wire connector, eight foot long, part number h20046. You see the seven pole and we have our wires. Once thing to know about this is that the functions do not match the colors better on the trailer. Now on the other side of the box well go ahead and replace them with solid grommets with a hollow grommet and well go ahead and run that over our wire that we can go ahead and push the wire back into the box. Then well go ahead and add our ring terminals to our wires. Now well go ahead and start attaching our wires, well start off with the green wire from the seven-pole which will be our running lights; this will be connected to the post with the brown wire from the trailer lights. The brown wire will be our right turn so that it will be connected to the post with the green wire from the trailer lights. The red wire will be the left turn function on the seven-pole, so well connect that to the post with the yellow wire from the trailer lights. Our blue wire will be our brake control power, so well hook that up to the post labeled blue. Now our yellow wire is usually reserved for reverse light or whatever function youd like. However, this application is not being used, so well just ignore that wire. Our black wire will be our 12 volt power supply, however this trailer is not using it right now, but well keep it to the junction box for our upgrade in the future. Well now go ahead and take our white wire push it to the ground from our towing vehicle that will be transferred to the trailer and well connect that back up to the white post, well get two white wires. With all of the wires in place well go ahead and tighten down the nuts. Next well go ahead and install the clamp from the wires that come in from the trailer side. Looking at the box on the left hand side there is provision for a clamp. Well make sure everything is pushed together properly and wont get pinched, well go ahead and install the cover. Well fasten and replace of these two bolts. Thats what it takes to install our junction box. All right with that it will finish it for our install of part number 38656, a trailer line junction box on this new trailer.

Customer Reviews

Trailer Wiring Junction Box - 38656

Average Customer Rating:  4.8 out of 5 stars   (694 Customer Reviews)

This Spectro trailer wiring junction box provides a fast, easy way to connect the wires from the trailer connector to the wiring for either a 6-way or 7-way connector. Makes replacing your trailer's connector simple.


I needed a way to reorganize wiring for my very old utility trailer. This wiring junction box from etrailer met my needs exactly and made my re-wiring project easy

It works well to organize wiring.
Dale P - 07/14/2022


This junction box was exactly what I needed. Had a short from cable wear and needed to splice on a new pigtail. This box made it super easy and really clean.


I was able to replace a residential electrical box with this Junction Box. The residential box was mass of wires with wire nuts that are not suitable for a 5th wheel trailer. Also, it was almost impossible to track wires when troubleshooting an electrical issue. It is a shame that Forest River would build RVs that could become such a dangerous situation if wires become lose(i.e. Brakes, etc.). Wire Nuts are not to be used in an environment subject to vibrations . I cam now trace my wires with ease, if needed.

Since I installed this box, I have not had any issues with brakes, lights or charging systems from the truck or 5th Wheel Trailer. I am very happy with the results.
BBMUSE - 02/08/2022


Installed in about 30 minutes, made install a breeze and took the mess out of a rats nest of wiring spliced under the trailer. Comes with plenty of grommets and all hardware to put together. You need to supply the bolts or screws to mount this to your trailer. Each terminal is labeled for what connects to it taking the guess work out of matching wires up.

Still works great, no issues at all.
Richard P - 10/14/2018


Rewired my trailer and used this junction box to go from my main cable to all the individual lights and brakes. It worked great, the only thing I didn't like about it was that it only had two cable clamps on the inside

I still have all the electric supplies from etrailer on my cargo trailer. I have had no issues with any of your products whatsoever. I hope this helps
Chris B - 11/11/2017


Had to replace my 7 PIN plug and found the old one was crimped onto the trailer wires, URGH. So trimmed all the trailer wires and terminated them in this box. Made connecting my new plug much better.


It is going to serve the intended purpose of gathering all these wires into a controlled location. The only drawback is the labelling on the box for the wire locations is extremely difficult to read. Not a big deal.


Simple easy and effective. This isn't the first time I've used this style of junction box, but they definitely make wiring any size trailer soon much easier.


We wanted both a 7-wire and a 4-wire plug on the same trailer. This junction box made the installation very easy. If your connecting the Hopkins 7-wire harness to this box, you'll probably have to ignore the wire colors names and just use the location (R Turn, etc.). Both are marked on each terminal.

There are 5 different openings to choose from to route the wiring to this box and it comes with both rubber grommets to run wiring through and rubber plugs for the openings not used. A downside is that only the side with 2 openings has wire hold downs on the inside. It would have been nice if at least the opening on the opposite end also had such a feature.

It's fairly water tight and installed easily onto the frame, under the trailer. Because it's lightweight plastic, I'm not so sure how long it'd last in the direct sunlight if it was mounted on the tongue or other exterior location.


This trailer was built from scratch using only the metal frame. I purchased some items from etrailer an was very satisfied with the products.

Great job! Looks like a high quality build.
-- comment by: Mike D - 03/26/2015

Its still working great.
Wayne M - 08/07/2015


This box was used as part of an electric brake conversion on my trailer. This box was an excellent means of connecting the existing wiring and the new brake wiring into the new 7 way trailer connector. It has the required breakouts and grommets needed to make the wiring task the easiest part of the conversion.

For a neat install and ease of replacement later if necessary, theres no better way to go than a junction box.
-- Etrailer Expert Mike L - 07/25/2019
Im very satisfied with this connection box. It keeps all of the connections well insulated and out of the weather.
TomD - 07/24/2020


Junction box was perfect for my applica tion...thanks.....


I love these boxes. I've repaired numerous trailers my sons and I own, including cargos, flat beds and horse trailers. I really like the grommet locations, cable clamping and posts for wire connections. There is plenty of room inside to neatly route wires.


Junction box was great had it installed and wires hooked up in a little over an hour. Service and shipment was better than expected. Will definitely use etrailer for more of my needs, very good company. The only thing that took a while was the molded seven connector wire colors don't all follow standards, but a test light and a few minutes and it was figured out.


Now I have a chuckwagon that is all tricked out for side marker lights and more. This box really did the trick for keeping wires organized.


First things first. Love your company! Keep up the great work. etrailer has been my go to site for all my trailer needs. As for the break away kit. I got a used inclosed trailer and it had a very large truck battery inside the trailer with a very large hole in the floor for the trailer breakaway system. An eye sore to say the least and very much in my way. I was shopping around etrailer site found the Bright way breakaway system. Watched the review about it. Did not think it would work for my two axle brake system. Ordered it anyway. Installed on outside of trailer. Did all this after installing new brakes. Did a test and I could not get the wheels to turn with trailer off the ground as well as doing a test with the trailer on my truck and the breakaway system worked and held the truck in place. Bottom line is the system does it job for a small battery. Love the system. It is small, can be placed almost anywhere, and again does its job. Only issue I had with it was the two screws that hold the cover closed started to rust after the first time it got wet. I replace them with better ones.


I purchased this product after researching current trailer rewiring methods. I recently had my entire 18' trailer wired and upgraded. The trailer is 8 years old and I wanted to replace the original 4 way trailer harness which the trailer manufacture had surrounded in electrical tape which also needed an adapter. After some research, I opted for this 7 way pigtail (50-67-005) which is the connector I needed my trucks and this junction box. (all contacts were current)
The junction box is sturdy and well made, we installed 7 way wire within the box with a snug fit. The trailer now has a clean professional appearance and most test functions can be performed from the junction box location. The junction box was installed behind the trailer tongue frame to minimize the weather elements. This product appears to seal well as the product description indicates. I am very satisfied with this product and Etrailer's customer service.


I am very happy with this heavy duty J-box. The smaller one I was trying to use didn't have adequate space or heavy enough terminals for the size wire needed for the brakes on my trailer. Leave it to etrailer, they always come through for me and are an absolute pleasure to deal with, especially Danielle!!!


Well made product with a great design. The only criticism I have of the product is the cheap flat head screws provided with it. They should be stainless and the smaller ones Phillips head. If the screws were of be it would have gotten a five star rating.


Installed as I had planned and it went well. Wired the supply line to the box to all of the correct wiring terminals as it is labeled in the box. I was prepared by other reviews, things may not match up, which they didn't, but no biggie. Once I flipped a few wires around things worked nicely.


Lots of room to add more connections.


I'm renovating my old Apache camper and this Junction Box made the job so easy and in looks great, too. Plenty of lugs for all my needs and one or two spares. Purchased the 7 pin trailer light cord as well. Now I have all new camper wiring to hook up to my new pick-up!


Thanks for your help with parts for my trailer build. My wife and I are still making custom cabinets out of curly maple. We hope to finish this winter. We have taken it out 7 times this season. Thanks again.


etrailer is a great web-site . Has helped me a lot with trailer brake wiring and brake controller wiring , their products are top notch .
Bought the junction box to replace mine as it is an open air terminal strip and gets corroded from the road grime and rain , these boxes are nice for troubleshooting trailer lights with a simple hand held meter and they are weather tight .
Have built my own in the past but cant beat this box for price .
Have not installed it yet , replacing the trailer floor at the moment and updating the wiring and paint .
Excellent product .

Works good , was having trouble with my car trailer lights , easy to troubleshoot now with this junction box
Crankshaft J - 02/03/2021


Had some real issues with this one. Should have noticed when purchasing this harnes is not wired using standard truck/trailer color format. Other than that it went together fairly nice. If the connector would come apart I was thinking of fixing the wiring my self.

Show More Reviews

See what our Experts say about this Spectro Accessories and Parts

  • How Do the Wires Connect to the Pollak 11609-EP / Junction Box and Is It Water Proof
    The connections on this Trailer Wiring Junction Box, part # 38656, are made on the inside of this junction box with ring terminals. The wires will travel through the rubber grommets to enter and exit the box. This box is weather proof, but not water proof, and what that means is that it will keep rain out under normal circumstances, but if it were to be submerged the box would not be dry on the inside. My contact at Pollak said that you could probably apply a rubber sealant to the lid...
    view full answer...
  • What Are The Dimensions Of The Trailer Wiring Junction Box
    The dimensions of the trailer wiring junction box, product # 38656 are, length 7 inches, width 3-1/2 inches, height 2-1/4 inches and the mounting flange distance is 7-3/8 inches on center and is 8 inches overall. Mounting flanges are 1/4 inch thick plastic.
    view full answer...
  • Can the Trailer Wiring Junction Box # 38656 be Used with a 4-Way
    You could use the Trailer Wiring Junction Box # 38656 on a trailer with 4-way wiring. You would just have a few extra pins available on the box that you wouldn't end up using.
    view full answer...
  • Distance Between Mounting Holes on the Junction Box part # 38656
    The mounting holes of the Junction box part # 38656 that you referenced are 7-3/8 inches apart and are 1/4 inch in diameter.
    view full answer...
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  • What is the Inside Diameter of the Grommets Included with the Spectro Junction Box # 38656
    The grommets included with the Spectro Junction Box, # 38656, have an inner diameter of .603 inches. These grommets would definitely be too small for your larger output cable and would be a tight fit with your input cable. I checked our other junction boxes and they each use grommets with the same inside diameter. These junction boxes were designed to work with coated 7-wire trailer wiring which has a diameter of .59 inches. You could possibly trim the grommets. They are .20 inches thick,...
    view full answer...
  • Can a Trailer Wiring Junction Box Be Used on a Trailer with a Battery and Power Inverter
    The junction box part # 38656 is a great way to organize trailer wiring on a trailer. There's no reason you couldn't use this with what you are trying to do. You would have to run the 12 volt accessory circuit of your trailer's connector to the junction box and then from there to the battery of the trailer.
    view full answer...
  • Can a 12 Volt Accessory Circuit be Used on the Spectro Junction Box For Trailers part # 38656
    The Spectro Junction Box part # 38656 can have a 12 volt accessory circuit added to it so that you could put a maintenance charge on your trailer battery but it does not have a specific pin to use for this circuit. You would just need to pick an un-used pin in the box and run the circuit from the 7-way to it and then from it to the positive post of your battery.
    view full answer...
  • What Circuit of a Trailer 6-Way Should a Battery Maintainer Get Power From
    Yes, the battery maintainer you have requires a 12 volt power source coming straight from the battery and the center pin of your 6-way is exactly that so it would work very well for you.
    view full answer...
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  • Testing Trailer Lights and Electric Brakes without Connecting Trailer to a Vehicle
    If you have a separate car/truck battery you could apply power to each of the pins on the trailer connector (or the wires directly some point behind the connector) and that should power on whatever is associated with a given pin.
    view full answer...
  • No Right Side Stop or Turn Signals On Trailer
    In order to check the right hand brake/turn signal circuits on your trailer you will first want to obtain a twelve volt battery and then hook a hot lead up to the pin on the trailer connector which is responsible for the right hand brake/turn signals (see article). Once this is done you will need to also obtain a circuit tester and begin probing the right hand brake/turn signal wire behind the trailer connector, working your way back as best as you can to see where the power stops. I would...
    view full answer...
  • Purpose of Trailer Junction Box
    The # 38656 Junction Box won't take the place of a trailer mounted battery, but it provides a protected and organized method of connecting the wires from the trailer connector pigtail to all the various lighting, power and brake circuits on the trailer. If you watch the linked video, you can see exactly how they're used.
    view full answer...
  • Junction Box Recommendation for Camper Trailer
    Sounds like you are looking for a junction box for your trailer. For that we have the part # 38656 which would work well for you. I attached an install video for this for you to check out as well.
    view full answer...
  • Troubleshooting Trailer Brakes that are Always Engaged
    First of all did this problem just start happening? If the trailer has always worked fine before on the same truck then it's likely a short on the trailer's brake wiring. I would start by cleaning the connector and make sure it's free of any debris or corrosion. Also make sure the breakaway pin is inserted properly. However, it the probem is from the breakaway switch the brakes will only be locked until the breakaway battery dies. If both of these are fine then you need to inspect...
    view full answer...
    Image 1 for
  • Wiring Electric Brakes to Trailer Without Access to 7-Pin Wiring on Trailer
    Yes, it doesn't matter which wire is ground and which one is the power wire coming from the brake assemblies. If you have a brake wire on each side of the trailer, you do not have to splice. You can use a brake wire for each side. Since the trailer is aluminum you cannot just ground to the frame because it does not conduct electricity well. The aluminum trailer probably has a hard metal core which is why the manufacturer was able to ground into the frame with screws. You won't be able...
    view full answer...
  • What Pin Does Brake Output Circuit of Trailer Attach to On Junction Box 38656
    The terminal labeled "stop" is the correct one to connect the brake output circuit of your trailer wiring to. This would be the one fourth from the left. I attached a picture that shows all of the terminal labelled for you to check out as well.
    view full answer...
  • Grounding Brakes for New Installation on Trailer
    You can route the grounds from your brakes to your junction box like part # 38656 but most people just ground the brakes to the trailer frame. The frame is a ground which is why this can be done, just make sure that it is a secure connection to a clean surface. Your brake assemblies will have 2 wires that are the same color. It actually doesn't matter which wire you use for power and which one you use for the ground.
    view full answer...
    Image 1 for
  • Wiring Diagram for Trailer Wiring 6-Way
    Assuming your 6-way was wired up using industry standard trailer wire colors you should use the chart I attached that shows how to wire up the 6-way. Use the orientation of the screw on the center pin to know which direction is "up" and down on the diagram.
    view full answer...
    Image 1 for Image 2 for
  • Could Breakaway Battery on Trailer Power A-Frame Trailer Jack
    A breakaway battery won't have the amperage to power an electric jack most likely and even if it could you really need to keep the breakaway battery fully charged at all times so that in emergency situation when needed it will be able to do it's job. You'd want to have a deep cell battery installed on your trailer or possibly power the jack from 12 power source from 7-way trailer connector.
    view full answer...
  • Replacement Junction Box for Southland Trailer
    I do have an option for you but the junction box lid's aren't universal so the only way to make sure you get a new one is to replace the entire junction box with one like the Trailer Wiring Junction Box part # 38656.
    view full answer...
  • Why Are My Trailer Brakes Activating/Deactivating When Plugged In/Unplugged to 7-Way Plug?
    If you are experiencing power at the 1 o'clock position on your 7-way, the issue most likely lies with the trailer's wiring. With this situation, it is important that the trailer wiring is correctly inserted into trailer's side 7-way plug so that the correct pins on the vehicle side can activate the correct corresponding pins. All that being said, I recommend removing your trailer's 7-way and using the Junction Box # 38656 to make sure that the wiring is on the correct pins on the trailer's-side...
    view full answer...
    Image 1 for
  • Draw Tite Gooseneck/5th Wheel Connector # 20027 Recommendation on a 1997 Chevy C/K Series Pickup
    The absolute easiest way to accomplish this task would be to use a Draw-Tite Wiring Adapter, part # 20027. You would simply plug this into the 7-way that is at the rear of you 1997 Chevy Silverado and then run the 7-way end up to the bed and mount it in a location that is easily accessible for your gooseneck. You will probably want to use some zip-ties to secure it in such a way that it will be accessible when not in use and not drag on the ground. You could make the Trailer Wiring Junction...
    view full answer...
  • Recommended Wiring Junction Box For Utility Trailer
    If you are wanting to secure the wiring on your trailer and keep it secure I recommend using a wiring junction box like part # 38656 on your trailer. You can place the junction box on the tongue of your trailer and run the wires from the trailer into one side of the box and on to the terminals. Then attach the trailer connector with wires cut to the appropriate length to the matching wires on the terminals inside the box and extend it so you can attach it to your vehicle. You want...
    view full answer...
  • Using Tow Ready # 118158 Converter to Install Third Brake Lamp on Trailer
    To wire a functional third brake light, a tail light converter such as the one you mentioned would be used. On the input side, the green wire would tap into the right turn circuit, and the yellow wire would tap into the left turn. On the output side, the yellow and green wires would be capped, with the third brake lamp being fed by the red wire. Make sure the third brake lamp is correctly grounded to the trailer frame either by its mounting bolts or by a jumper grounded to the trailer...
    view full answer...
    Image 1 for
  • Should an Electric Trailer Jack Run Off of a Trailer Breakaway Battery
    The trailer jack should very much NOT be powered by the breakaway battery. That was likely done by the previous owner for convenience. The breakaway battery is a dedicated battery for the breakaway system only. It needs to be able to apply the trailer brakes on full for 15 minutes. If the jack was to run down the battery then the breakaway system would not be able to power the brakes for long enough. Also, a breakaway battery is too small for the power needs of a jack. Most breakaway...
    view full answer...
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