Roadmaster Brake-Lite Relay Kit for Towed Vehicles
(483 reviews)
Price: $34.35
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Roadmaster Brake-Lite Relay Kit for Towed Vehicles
Item # RM-88400
Retail:$45.90
Our Price: $34.35
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Roadmaster Tow Bar Braking Systems - RM-88400
- Brake Light Relay
- Roadmaster
Relay works with your tow bar wiring system to ensure that your towed vehicle's turn signal lights flash in tandem with your RV's lights.
Features:
- Keeps your towed car's brake signal from overriding the turn signal sent by your RV
- Allows signal lights on towed car to flash in tandem with RV lights even when vehicle's brake pedal is depressed
- Required on towed cars with combined lighting if you are using a supplemental braking system
- Needed on applications with separate lighting if towed car is wired using a TrailerMate wiring harness or a 4-diode kit (instead of a 6-diode kit)
- Does not interfere with towed car's electrical system
- Activates automatically when RV running lights are turned on
- Includes all necessary components for standard installation
- May require additional connectors and length of wire for certain applications
- Limited Lifetime Warranty
The purpose of a brake light relay kit is to prevent your towed car's brake signal from overriding the turn signal that comes from your RV. When your towed vehicle is properly wired and connected to your RV, its indicator lights will illuminate as you engage the turn signals in your RV. However, if you have only a four-diode system in place, the turn signal will be overridden by your towed car's brake signal as soon as your supplemental braking system presses the towed car's brake pedal. As a result, drivers behind you know only that you're slowing down and not that you are turning.
Installing a brake light relay in your towed vehicle fixes this problem by ensuring that your car's brake signal does not override the RV's turn signal. Therefore, your towed car's lights will function in accordance with your RV at all times.
Is a Relay Required?
To determine if a brake light relay is needed to properly wire your vehicle to be towed, answer the following questions.
Are you using a supplemental braking system that depresses the brake pedal in your towed car?
No - You do not need a brake light relay.
Yes - You may need a brake light relay. Continue on to the next question.
Do the brake lights on your towed car illuminate while the engine is off?
No - You do not need a brake light relay.
Yes - You may need a brake light relay. Continue on to the next question.
Do your towed car's brake lights act as both the brake signals and the turn signals?
No - You may need a brake light relay. Continue on to the next question.
Yes - Your towed car has a combined lighting system. You will need a brake light relay to ensure proper activation of its signal lights.
Does your towed car have separate brake lights and turn signals?
No - Your towed car has a combined lighting system. You will need a brake light relay.
Yes - Your towed car has a separate lighting system. You may need a brake light relay. Continue on to the next question.
Are you wiring your vehicle with a six-diode kit or a TowDaddy custom wiring harness?
No - You will need a brake light relay to ensure proper activation of your towed car's signal lights.
Yes - You do not need a brake light relay.
Installation of the Roadmaster Brake-Lite Relay
Most towed cars require the normally open installation method. Ford and Lincoln models with neutral tow kits and most automobiles that have a push-button start function will require the normally closed installation.
Normally Open
The diagram and steps shown below demonstrate the installation for normally open applications. Be sure to follow the instructions included with your relay kit for a more detailed process.
- Remove the blue wire from the kit. This wire is not needed for normally open applications.
- Locate the brake-light-switch wire in your towed car.
- Remove the brake light fuse.
- Cut the brake light wire a few inches away from the "cold" side of the brake light switch.
- Attach the relay to the wiring for the RV braking monitor. The diagram above shows where the green wire attaches the relay to either a Roadmaster Even Brake or BrakeMaster system.
- Connect the black wire of the relay to the brake light wire near the brake light itself using the included blue butt connector.
- Identify a fuse that is only powered when the ignition is in the "run" position and not when it is in the "tow" position. Pull the fuse. Insert the fuse into the slot closest to the fuse blades, then insert the fuse tap into the empty slot in the fuse panel.
- Using the attached blue butt connector, connect the red wire from the brake relay to the wire from the fuse tap.
- Ground the white wire to your towed vehicle's frame.
- Secure the relay with the included wire ties.
Normally Closed
The diagram and steps shown below demonstrate the installation for normally closed applications. If you have a Ford or Lincoln that has a neutral tow kit or if your car has a push-button start feature that will not start the engine when the brake fuse is removed, then you need to perform a normally closed installation. Be sure to follow the instructions included with your relay kit for a more detailed process. Normally closed operations may require additional connectors and length of wire that are not included with this kit.
- Remove the green wire from the kit. If you are using a Roadmaster Even Brake supplemental braking system, set this wire aside to use later.
- Locate the brake-light-switch wire in your towed car.
- Remove the brake light fuse.
- Cut the brake light wire a few inches away from the "cold" side of the brake light switch.
- Attach the relay to the wiring for the RV braking monitor. The diagram above shows where the blue wire attaches the relay to either a Roadmaster Even Brake or BrakeMaster system. The green wire may be needed here.
- Connect the black wire of the relay to the brake light wire near the brake light itself using the included blue butt connector.
- Use a voltmeter to identify the wire in your aftermarket light harness that is conducting the tail light signal. Typically, this is a brown wire.
- Using a 16 - 14 gauge butt connector (sold separately), attach a section of 14-gauge wire (sold separately) to the end of the red wire. Trim the new 14-gauge wire and connect it to your aftermarket wiring harness.
- Start your engine and turn on your headlights. Test the tail light wire with a voltmeter. If your voltmeter doesn't register any voltage, move on to step 10. If 12V DC registers, you will need to install a single diode (RM-790; sold separately).
- Ground the white wire to your towed car's frame.
- Secure the relay with the included wire ties.
88400 Road Master Brake Light Relay
Installation Details
Customer Satisfaction Score:
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Customer Reviews
Roadmaster Brake-Lite Relay Kit for Towed Vehicles - RM-88400
Average Customer Rating: 4.8 out of 5 stars (482 Customer Reviews)
Relay works with your tow bar wiring system to ensure that your towed vehicle's turn signal lights flash in tandem with your RV's lights.by: Richard10/24/2017
Evidently Roadmaster had made some slight alterations from the depiction, for the better. The fuse wiring was a spade end with two fuse holders built in. The holder closest to the spades was for the original circuit and the other for the new circuit. This was very handy. I had watched the installation video and thought it would be fairly easy; therefore I attached the terminals to the green, black, and white wires before even going to the CR-V.
I did however purchase different spade connectors as I thought I may want to remove the brake relay switch in the future for another vehicle should I trade. Also the yellow connector is quite large and the video showed bending the wire over itself so that it would hold on the smaller wires. This was a wise decision.
What was the problem was the wiring in my CR-V. The video showed similar size wiring from the brake switch. What I found was smaller wire, loomed very close to the brake switch. Evidently Honda had made some modifications. I believe the wire was 22 gauge and there was no real way the blue or yellow connectors would have worked. That said, after disconnecting from the switch, stripping the loom back to get some exposed wiring, cutting and using the 22-16 gauge connectors, drilling a hole for the ground screw, etc. the switch worked perfectly.
I did vary the fuse location from the 7.5 Amp #29 Occupant Detection System (ODS) to the 15 Amp #28 Washer as I figured it would less likely interfere with any operation.
Comments
Working great with no problems.
Richard - 10/24/2018by: Doug 08/11/2023
I used this on a 1988 Toyota Land Cruiser, so I could flat tow it behind an Motorhome. Easy to install!
by: Jeffrey12/22/2021
I have successfully completed the installation of the following items that I purchased from etrailer:
> Nighthawk RM-676 tow bar
> RM-524458-5 base plate
> DEMCO Stay in play DM86VR
> RM-152 diode wiring kit
> RM-156-25 charge wire kit
> RM-88400 brake switch relay kit
I work slow but methodically. I had no issues other than the high degree of difficulty for a 68 y/o man working alone. This project exceeds the abilities of someone NOT mechanically inclined. There is also the need for some specialty tools. I found that feeding the wiring through the dash, firewall, and underbody was more difficult than installing the front baseplate. Overall, I am satisfied with the function of this installation. I am glad I did it myself rather than having it done.
Tow vehicle: 2021 Entegra Emblem 36U
Towed vehicle: 2018 Ford Fusion Platinum Energi
Comments
The performance of this tow bar and associated hardware has been outstanding! Service and warranty follow up service from Roadmaster has also been outstanding! I am very satisfied with my purchase.
Jeffrey - 11/19/2022by: Michael 08/06/2023
It was a little tricky to install but easy to adjust the switch setting for precise response to brake pedal movements. Instructions were easy to follow follow and accurate.
by: Donald05/26/2023
We tow a 2022 Ford Escape behind our Winnebago motorhome. This wiring kit did the job for us. Everything working great!
by: Charlie 07/05/2023
Good kit. Includes everything you need. Good instructions. Continues to work perfectly after one year and many towing sessions.
by: Richard 07/13/2023
Works great, but you need to be a contortionist to get behind the brake pedal to access the wires to cut this in.
by: Hans04/13/2022
Fairly easy to install, especially with the aid of the etrailer videos, and it works great on my 2016 Wrangler
Comments
After a year it still works great.
Hans - 04/17/2023by: Andrew 08/08/2023
Needed this for my F150 flat towing
by: Troy05/21/2023
Installer did not get this installed correctly. Figuring out if it was needed or not was an ordeal. Lost of conflicting information in the product description and on website. It was needed and doesn’t work correctly, but I don’t think it’s the products fault. Make sure you get a competent installer.
by: Garry07/12/2023
Excellent product. Delivered on time, all my questions were answered. Great company I would recommend to anyone.
by: Kim12/28/2022
Thank you for including the fuse.
Oh my! Testing for that brake light. I finally found a tool where one person could handle testing and then pressing on the brake pedal a normal probe DC tester was impossible for me to use. Be ready to do some under the dash yoga poses!
The parts for this don't quite match the video, once again look at the diagram to verify. But once installed it worked for the tests (don't forget to ground), now to get rolling.
When ordering this spend the extra money on a Hook Probe Circuit Tester Item # PTW2993
by: Kenneth 06/27/2022
Easy to install. Easy to remove. Tows great. No problems at all. Pulling with our Thor Palozzo.
Comments
No problem
Kenneth - 06/28/2023by: Richard01/19/2023
I haven't installed this & won't get to it till the end of February. Do you have a video outlining this installation?
Comments
We do! At the top of the product page, below the pictures, you will see the multiple install videos we have posted to help our neighbors, like you!
-- 
Brooke M - 01/23/2023by: Denny11/02/2022
Outstanding product and even better customer service! Two backyard mechanics installed baseplate and braking system with just one call to confirm proper wire connection. Total package works great.
by: Larry 03/21/2023
Had no problems on installation expecially watching the video
by: James10/13/2022
As with any somewhat universal kit, there are going to be a few things that need sorting out. First, the wire tap that comes with the universal wiring kit (84000) had the wrong size wire tap. It was for the mini where my 2018 ford F150 had really small fuses. So I had to order a different wire tap to fit into the fuse box for the brake relay. No big deal.
by: Lee02/11/2021
I used this relay along with a separate switch to turn on Firestone air suspension compressor. Remember always use electric grease on connections. Thank you etrailer. God bless. Jesus saves.
by: Ed02/24/2023
Works great to flat tow our wrangler using the the d- ring mounts
by: Tom06/18/2023
I decided to not install this. Still re turnable?
Comments
I am sorry as it would be too far past our 60 day return policy to allow the return.
-- Jenny N - 06/19/2023by: Don 04/13/2023
Easy install especially with included fuse tap.
by: Robert09/07/2023
Simple install
by: Clyde11/25/2022
We were at a stand still. Wiring the lights from my motorhome to my ford pickup. Sheryl saved the day, without hesitation, she described just what we needed.
Always turn to etrailer for hitch, electrical and all towin needs. Never let me down.
by: Scott12/28/2022
Parts arrived on time and as promised. Easy install. Love etrailer’s detailed installation videos!
by: Greg02/15/2023
Great product,very happy how well this unit works in our CRV. Install was very easy,the instructions were spot on.
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See what our Experts say about this Roadmaster Tow Bar Braking Systems
- What is the Purpose of the Roadmaster Brake-Lite Relay Kit Part RM-88400The Roadmaster brake relay kit # RM-88400 you referenced will prevent your 2014 Honda CR-V's brake signal from overriding the turn signal sent by your RV. It's only active when you depress the brake pedal. If the brake light relay isn't installed, the supplemental braking system that you are using will depress the CR-V's brake pedal which will activate the brake lights and override the turn signal. It's illegal to have vehicle brake lights override the turn signal from a motorhome.
view full answer... - Troubleshooting Vehicle that Won't Shift Out of Park After Roadmaster Brake Lite Relay InstallI spoke to my contact at Roadmaster and they have seen the problem you are describing and it means one of two things. Either the wires from the brake light relay are making a bad connection or the brake light wire that runs from the relay to the interior of the tow vehicle has shorted out and has blown the stoplight fuse and that is why. Check the brake light fuse. If it is blown the second scenario I described is what is happening. You would need to track down the short that is causing...
view full answer... - Will the Brake-Lite Relay # RM-88400 Interfere with the Auto Start Feature on a 2013 Honda CR-VI spoke with my contact at Roadmaster and he told me that the Brake-Lite Relay, # RM-88400, will not interfere with auto start feature on your 2013 Honda CR-V. The Brake-Lite Relay connects to the blue brake light wire wire coming from the brake light switch that powers the brake lights. It does not connect to the circuit that shuts off your engine to prevent theft. When installing the Brake-Lite Relay on your vehicle, you will want to follow the Standard (Normally Open) Installation...
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- Does a 2012 Ford Focus Need a Brake Light Relay for Flat-TowingTo determine if you need a Roadmaster Brake-Lite Relay Kit # RM-88400 you will need to answer the following questions: Are you using a supplemental braking system that depresses the brake pedal in your towed car? No - You do not need a brake light relay. Yes - You may need a brake light relay. Continue on to the next question. Do the brake lights on your towed car illuminate while the engine is off? No - You do not need a brake light relay. Yes - You may need a brake light relay....
view full answer... - When Installing Brake Light Relay on a 2013 Ford Edge Should it Be Normally Open or ClosedI looked through an online copy of the owners manual for the 2013 Ford Edge Limited and the #59 fuse looks to me like the only one you would need to pull. If the vehicle still starts then you would need to go with the normally open instructions for brake light relay # RM-88400. I have included a picture showing how it is set up normally open.
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view full answer... - Is a Roadmaster Brake-Lite Relay Kit # RM-88400 Needed when Flat Towing a 2011 Ford FlexTo determine if you will need a Roadmaster Brake-Lite Relay Kit you will need to answer the following questions: Are you using a supplemental braking system that depresses the brake pedal in your towed car? No - You do not need a brake light relay. Yes - You may need a brake light relay. Continue on to the next question. Do the brake lights on your towed car illuminate while the engine is off? No - You do not need a brake light relay. Yes - You may need a brake light relay. Continue...
view full answer... - Preventing Flat Towed 2012 Wrangler Brake Light From Overriding Coach Brake SignalIf you turn the ignition key of the Wrangler to the Towing Position, and you step on the brake pedal and the brake lights light up, you will have interference problems. I believe removing the stop light fuse would accomplish what you are trying to do, but the danger there is remembering to replace the fuse when you are ready to drive the vehicle. If your memory is anything like mine, this might be a bad idea, which is why we recommend using a Brake-Lite Relay Kit for Towed Vehicles, part...
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- If Taillights of Vehicle are Bypassed for Tow Bar Wiring is a Brake Light Relay RequiredIf the taillights of your 2014 Honda CRV are not being used in conjunction with your tow bar wiring then you would not need to use a brake light relay. Since they are being bypassed a brake light relay like part # RM-88400 would not be needed.
view full answer... - How to Determine if a Brake Light Relay is Required to Flat Tow a VehicleTo determine if your 2014 Jeep Grand Cherokee will require a brake light relay like part # RM-88400 you need to answer the following questions: Are you using a supplemental braking system that depresses the brake pedal in your towed car? No - You do not need a brake light relay. Yes - You may need a brake light relay. Continue on to the next question. Do the brake lights on your towed car illuminate while the engine is off? No - You do not need a brake light relay. Yes - You may...
view full answer... - When is a Brake Light Relay # RM-88400 Needed and How to Wire One in 2007 Chevy CobaltThank you for your multiple recent purchases from etrailer. We appreciate your confidence in us and your repeat business. Thank you also for your included photo. There is a straightforward question/answer process to let you determine if a brake light relay is required for any particular flat-towing application: Are you using a supplemental braking system that depresses the brake pedal in your towed car? No - You do not need a brake light relay. Yes - You may need a brake light relay....
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- Brake Lights Not Working After Install of RM-88400If you have a flat tow wiring kit with diodes, then you need the Roadmaster # RM-88400 Brake Light Relay Kit. It is normal behavior for those lights not to work when the wiring kit is active. We want the towing vehicle (through the wiring kit) to control those lights.
view full answer... - How To Prevent A Towed Vehicle Brake Light From Overriding The Signal From The MotorhomeYou're needing a Roadmaster Brake-Lite Relay Kit for Towed Vehicles # RM-88400 to prevent your 2016 Ram 1500's brake signal from overriding the turn signal that comes from your RV. When your towed vehicle is properly wired and connected to your RV, its indicator lights will illuminate as you engage the turn signals in your RV. However, if you have only a four-diode system in place, the turn signal will be overridden by your towed car's brake signal as soon as your supplemental braking system...
view full answer... - Installing the Roadmaster Brake-Lite Relay Kit on a 2017 Ford F-150, is the Green Wire NeededWhen we did the installation of the Roadmaster Brake-Lite Relay Kit # RM-88400 on a 2017 Ford F-150, the green wire was not needed. The only reason you would need the green wire is if your supplemental braking system is the Roadmaster Even Brake system. The black wire that is connected along with the blue wire is the wire that will go to the brake light signal that is run up to your RV and likely connected using the 6-way connector.
view full answer... - Installing The Roadmaster Brake-Lite Relay Kit On A 2021 Ford Escape HybridThe purple/white brake light switch wire is going to be located under inside the dash above the brake pedal. This will require you to remove portions of the dash to gain access and install the Roadmaster Brake-Lite Relay Kit for Towed Vehicles # RM-88400. I've attached a video where Connor will help walk you through this installation.
view full answer... - Installing The Roadmaster Brake-Lite Relay Kit On A 2020 Ford RangerYes, when installing the Roadmaster Brake-Lite Relay Kit for Towed Vehicles # RM-88400 you should have wired it based on the "Normally Closed" diagram since you have a Ford with neutral tow.
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- Roadmaster Brake-Lite Relay Kit Installation On A 2021 Ford EscapeThe brake light switch wire is a single wire that is white and purple. It will be located towards the top of your brake pedal assembly so you may need to remove a portion of the dash to access this wire.
view full answer... - Installing The Roadmaster Brake-Lite Relay Kit On A 2016 Ram 1500Before installing the Roadmaster Brake-Lite Relay Kit for Towed Vehicles # RM-88400 you need to determine if your 2016 Ram 1500's system is normally open or normally closed. If your car has a push-button start feature that will not start the engine when the brake fuse is removed, then you need to perform a normally closed installation. If your Ram is a normally open system you'll complete the following steps: 1. Remove the blue wire from the kit. This wire is not needed for normally...
view full answer... - Installation of Roadmaster Brake-Lite RelayIt sounds like the Roadmaster Brake-Lite Relay Kit for Towed Vehicles # RM-88400 has possibly gone bad; if there was enough current to blow a fuse, it's possible that it also caused the relay to go bad. There are detailed instructions linked to this answer and you'll need to determine based off the vehicle you're towing whether or not you will install it normally open or normally closed- there are also diagrams and instructions on the product page.
view full answer... - Instructions for Roadmaster Brake-Lite Relay Kit # RM-88400 on 2017 Jeep CherokeeFor the install of the Roadmaster Brake Lite Relay part # RM-88400 for your 2017 Jeep Cherokee the most specific install instructions we offer would be the install video I attached that shows the kit installed on a similar 2018 Cherokee for you to check out. I also attached an install instructions link for this for you to check out but they are universal instructions that are not specific to your vehicle.
view full answer... - Installation of Diode In Roadmaster Brake Light Relay Kit on 2020 Ford F-150If you have a Ford or Lincoln that has a neutral tow kit or if your car has a push-button start feature that will not start the engine when the brake fuse is removed, then you need to perform a normally closed installation which involves using a diode-which I believe is the process you're referring to. I've linked a photo that shows the diode installation when using the Roadmaster Brake Light Relay Kit # RM-88400 that you can refer to, but you will splice into the brown wire on the 4...
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- Installation of Roadmaster 88400 and Locating Cold Side of Brake Switch on 2021 Jeep WranglerI've attached an installation video of the Roadmaster Brake Light Relay Kit # RM-88400 for you to have a look at on a similar Jeep Wrangler, where it details the process and where you can find the cold side of the brake light switch to tap into. You will need to remove the panel under the steering wheel to gain access to this.
view full answer... - Troubleshooting Inconsistent Tail Light Functions for Flat Towing 2004 Jeep LibertySince you installed the wiring on your 2004 Jeep Liberty a few years ago but never used it then the first thing to do is apply 12V power to each pin on the front of your Liberty to see if the lights function like they should. If they do then you know the problem is on your motorhome but if they don't then the problem lies with the wiring on your Liberty. Regardless which side it's on you'll want to use a circuit tester to test along the wiring to see where the signal gets lost. Making...
view full answer... - Is the Brake-Lite Relay Kit Needed for a 2017 Chevrolet EquinoxThe Roadmaster Brake-Lite Relay Kit for Towed Vehicles part # RM-88400 is not required for a 2017 Chevrolet Equinox so you will be good to go without it. That said, to answer your question, this is a universal component so specific installation instructions will not be provided for any one particular make and model.
view full answer...
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