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Roadmaster Brake-Lite Relay Kit for Towed Vehicles

Roadmaster Brake-Lite Relay Kit for Towed Vehicles

Item # RM-88400
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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. Lowest Prices for the best tow bar braking systems from Roadmaster. Roadmaster Brake-Lite Relay Kit for Towed Vehicles part number RM-88400 can be ordered online at etrailer.com or call 1-800-940-8924 for expert service.
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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.


Standard Normally Open Installation for Roadmaster Brake-Lite Relay
  1. Remove the blue wire from the kit. This wire is not needed for normally open applications.
  2. Locate the brake-light-switch wire in your towed car.
  3. Remove the brake light fuse.
  4. Cut the brake light wire a few inches away from the "cold" side of the brake light switch.
  5. 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.
  6. Connect the black wire of the relay to the brake light wire near the brake light itself using the included blue butt connector.
  7. 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.
  8. Using the attached blue butt connector, connect the red wire from the brake relay to the wire from the fuse tap.
  9. Ground the white wire to your towed vehicle's frame.
  10. 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.


Normally Closed Installation for Roadmaster Brake-Lite Relay
  1. 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.
  2. Locate the brake-light-switch wire in your towed car.
  3. Remove the brake light fuse.
  4. Cut the brake light wire a few inches away from the "cold" side of the brake light switch.
  5. 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.
  6. Connect the black wire of the relay to the brake light wire near the brake light itself using the included blue butt connector.
  7. 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.
  8. 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.
  9. 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).
  10. Ground the white wire to your towed car's frame.
  11. Secure the relay with the included wire ties.


88400 Road Master Brake Light Relay

Installation Details RM-88400 Installation instructions




Customer Reviews

Roadmaster Brake-Lite Relay Kit for Towed Vehicles - RM-88400

Average Customer Rating:  4.8 out of 5 stars   (284 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:

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 - 10/24/2018


by:

Ordered and install base plate over a year ago and finally got to use it a couple of weeks ago because motorhome was in shop waiting on parts. Pandemic and supply chain issues. Anyway, the base plate and accessories work great. Dinghy tracks well. Hardly know it’s back there.



by:

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



by:

This wasn’t too bad to install. What it does is uses a relay to make the brake lights work only with the key in. Technically since you are already cutting into the brake light wire you could put in a switch and warning light (to remind you it’s off ) but this automates it so you don’t forget.



by:

The items were fine. The 2 stars are for etrailer service. The kit etrailer recommended to control the lights on my CRV was not the one I needed. etrailer's return policy simply sucks. Free shipping to me but then take back half of the $XX purchase price for the kit I did not need for the return. THAT IS A RIPOFF. I will do my ordering on [another website] from now on.



by:

Fairly easy to install, especially with the aid of the etrailer videos, and it works great on my 2016 Wrangler



by:

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:

Good quality. Good instructions. Difficult to install only due to the tight quarters inside the Jeep. Works great.


Comments
Still works great. No problems at all.
Dale - 03/17/2022

by:

No issues after a year. Lights on truck works great with a supplementary braking system.


Comments
No issues and all is working great
Michael - 02/13/2022

by:

Installation was straight forward thanks to your wonderful how-to videos.



by:

I returned this kit because I discovered that the vehicle I was towing already had Brake Light kit installed.



by:

Works as expected, with no problems. I am happy with etrailer and their customer interactions. I installed a Roadmaster tow bar and brakes on my Honda CRV two years ago. I had a problem and they helped me solve it with a new brake light relay kit. All parts of the install on the toad and motorhome are functioning perfectly.


Comments
Still working perfectly.
Hyatt - 05/16/2021

by:

Works great to keep our toad battery ch arged.



by:

Website video made for an easy install and has worked great for the last year.


Comments
Excellent
Andrew - 04/29/2022

by:

The telephone support was excellent. I can't rate the product since it hasn't been installed yet.



by:

Worked great good instructions



by:

Easy to install. Easy to remove. Tows great. No problems at all. Pulling with our Thor Palozzo.



by:

Service was great as usual and the sales staff was knowable and helpful. I will return a relay I didn’t need and a extra wiring harness.
I give etrailer 5 stars.



by:

I ordered all the parts required to safely flat tow out 2017 Jeep Cherokee Trailhawk from etrailer.com. The only part they didn't have was the Mopar Flat Tow Enhancement kit Jeep requires to flat tow this model.

Ordering from them was great, the website is easy to use and I was able to locate all the pieces compatible with my specific vehicle. The expert recommendations help my decision choosing the right parts. I ordered from etrailer even though I found some of the parts on other websites a little cheaper. I chose to pay a little more because of all the effort etrailer has put into installation videos and guides. I was very pleasantly surprised to learn from etrailer that they have a price match guarantee!

So my equipment consisted of the following

Mopar Flat Tow Enhancement Kit (from Jeep)

Roadmaster Battery Charge Line Kit for Towed Vehicles

Mighty Cord 7-Way RV Style Trailer Connector - Trailer End

WesBarg 7-Way, RV-Style Connector w/ 6' Long Coiled Cable Trailer End

Pollak Black Plastic, 7-Pole, RV Blade-Style Trailer Socket - Vehicle End

Hopkins Custom Tail Light Wiring Kit for Towed Vehicles

SMI Stay-IN-Play DUO Supplemental Braking System

Roadmaster Brake-Lite Relay Kit for Towed Vehicles

Blue Ox Alpha Tow Bar - Motor Home Mount - 6,500 lbs

Blue Ox Base Plate Kit - Removable Arms

Blue Ox Tow Bar Cover - Aladdin, Aventa LX, Aventa II


The installation videos are great but not all inclusive. Take the time to read the instructions that come with the parts. This is a major project, I took about 30 hrs over a full week but as you'll see in the pictures I took s few extra steps to make a cleaner look.

Some of those extra steps:

The base plate install requires the bumper be modified cutting off a flange on each side, I spray painted this to prevent corrosion.

In the install video of the baseplate on the drivers side they use an extra quick link (not included) to run the safety cable around the wiper fluid reservoir. I took the time to remove it and run the safety cable behind it.

I didn't want our nice new vehicle to look like it can be towed so I played the brake away switch and 7 way trailer plug behind the license plate, so when not being towed our vehicle looks great!

Some things to be aware of. The Brake air cylinder that mounts to the brake pedal with four bolts may need longer bolts, it did on our Jeep. Spend the money for weather tight heat shrink crimp fittings. The Hopkins wire harness was about 1.5 feet short to get to my plug location. Buy extra zip ties, electrical tape and split loom.

I recommend reading all the various installation manuals and watching all the videos because the various components integrate together and if you install one at a time you'll be doing a bunch of extra work.

The brake light relay is a real pain in the butt, not because of the hardware but because of the location of the brake light switch which is very hard to get to.

Overall I am very happy with the products and how the installation looks. We haven't towed it yet but do not expect any problems.







Comments
Still very happy with our purchase. We’ve towed over 10k miles and have had zero issues with our tow setup. I’ve shared my experience with several other RVrs and recommended your company for their needs. Thank you
Roy - 07/30/2018


by:

I have now installed the following on my 2017 Wrangler:
Brake light relay kit .
Hopkins Towed vehicle Tail Light wiring kit.
Blue Ox base plate.
Blue Ox Patriot Portable RF Braking System.
All of this has taken about 3 days of work spread out over a week or so. Overall it went well. Not too many surprises. Crawling around under a car at 71 is a bit of a strain but I'll get over it. I must say that Donna P. has been a wonderful source of great information and has stayed right on top of the process. eTrailer has been a great source for this project.

I would recommend you all with no hesitation.


Comments
I am still in love with the products. My only issue is having enough time to use them more.
John M - 06/15/2018


by:

Worked as expected.used on 16 jeep trailhawk for 2000 mi. Trip to east coast.very satisfied.



by:

I have a 2016 Jeep Wrangler Sport Unlimited 4 door, after I installed the Hopkins Custom Tail Light Wiring Kit for Towed Vehicles - HM56200, I found I had to install the Road-Master Brake Lite Relay for Towed Vehicles - RM-88400 , I'm using a supplemental brake system, when the brake is depressed with ignition off, the brake lights come on and cancel out any directional signal on my toad, installing the relay solved this problem. I watched the video and this was helpful. Installation took me a few hours, climbing under the dash was not an easy chore for me, I'm not as young as I want to be, had to purchase 16 gauge Red wire to run to Fuse box under the hood, also I recommend having extra wire ties to do this. I recommend both products, easy to install and good quality.


Comments
Products are working well, have not had any problems with the system
Rich L - 11/13/2017


by:

I installed this on my towed vehicle about a year ago. The initial installation went well and the instructions provided the necessary information on installation. After a year, I have not had any issues with the equipment and the car's break lights work as expected as both a driven vehicle and a towed. There are a number of ways to setup a towed, and once I decided on using the vehicle lights rather than a light bar, this kit was kind of a no-brainer. Also, during the past 12 months I have purchased additional items from etrailer and have always been satisfied with both the products purchased and the support from etrailer.


Comments
The system continues to work as expected. We always perform a light check when hooking up the vehicle and have not had any issues with these components.
Robert M - 02/04/2020


by:

Easy install



by:

Relay works as advertised - cuts power to my 2013 Edge brake lights (with the key in the off/or accessory position) preventing the Edge brake lights from overriding the coach brake/turn signals when my supplemental braking system pulls the Edge brake pedal down.

Bit of a chore to install, mainly due to close quarters under driver's side of lower instrument panel and forced to lay half way in/out of Edge over the door sill. Also, vehicle info on Roadmaster web site indicates the Edge brake light wire coming from switch is purple/white, but I found 2 purple and white wires on mine, both together in the same socket on the brake light switch. Guess it depends on one's color sensing, but one of mine was a lighter shade of purple and the other darker, more shiny. I spliced into the light purple one first and naturally it was the wrong one, so had to reconnect it and splice into the other one to make everything work. Not a biggie, but the mini fuse tap supplied in the kit will not work with the low-profile mini-fuses used in the Edge interior fuse panel - you have to use a regular mini-fuse.

FYI - 2013 Edge Limited, V6/FWD; Air Force One supplemental brake system; DEMCO RV Tow Harness wiring kit (9523100) for tail/brake light connections (plug in/no splicing); DEMCO baseplate and Blue Ox Towbar.


Comments
John, do you have to pull fuses in your Edge? If so, which fuses do you pull?
-- comment by: Mike H - 04/22/2014

The 2013 Ford Edge doesn't require a fuse to be pulled, but doing so will eliminate the need to cycle the engine. If you pull MAIN IGNITION # 28 in the driver footwell fuse box, you can skip the starting and running procedure at the end of the tow. To do this you can either the fuse to be removed or to install a fuse bypass switch like part # RM76511
Roadmaster FuseMaster Fuse Bypass - 13" - 20-Amp Mini-Fuse
$68.00
. If you don't pull or bypass this fuse, you will need to follow the engine start procedure Ford outlines in the manual. Ford also indicates in the manual that if the Edge is a 2.0L 4 cyl. you must use a tow dolly to keep the front wheels off the ground, no flat tow. If it is a 3.5L or 3.7L V-6, you can either flat tow with all 4 wheels down or on a trailer. No tow dollies with front up and rear down.

-- Etrailer Expert Patrick B - 4/23/2014

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Ask the Experts about this Roadmaster Tow Bar Braking Systems



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    To 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....
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    Thank 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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  • Instructions for Roadmaster Brake-Lite Relay Kit # RM-88400 on 2017 Jeep Cherokee
    For 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.
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  • Could Relay of Roadmaster Brake-Lite Relay Kit for Towed Vehicles Item # RM-88400 Get Damaged
    Yes, most likely you did damage the relay. The good news is it's a very common automotive type relay you could take to a local car parts store and they'd be able to get you set up with a low cost replacement.
    view full answer...
  • No Brake Lights With Ignition Off Using Roadmaster Brake-Lite Relay Kit On a 2010 Honda Fit
    I spoke with Roadmaster about the issue you are having with the Roadmaster Brake-Lite Relay Kit for Towed Vehicles part # RM-88400 on your 2010 Honda Fit. They informed me that if the brake lights do not illuminate while the brake pedal is pressed when the vehicle's ignition is off then the relay is wired incorrectly so you will need to review that portion of the installation instructions which I have attached for you. If you think the relay is bad then you can switch this out for just...
    view full answer...
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  • Does Installing Brake-Lite Relay in 2014 Ford Edge Require Tapping Into Tail Light Signal
    I reached out to Roadmaster, who told me when installing the Roadmaster Brake-Lite Relay Kit for Towed Vehicles # RM-88400 in your 2014 Ford Edge Limited with push-button start. This is what they told me: "You want a designated line for the relay. The load demand on the charge line is limited, so stay with the using the tail light circuit."
    view full answer...


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