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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.
Features:
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.
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.
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.
California residents: click here
Product was at a good price. It was shipped quickly and I received it promptly.
Etrailer is a great company to order from and I highly recommend them.
That said, the brake light relay performs exactly as it is supposed to. I am well pleased!
Does NOT work for 2021 and new F-150's. There is a lot of bad advice regarding this in the Q&A section that etrailer needs to update. Associates incorrectly have been including the Brake-Lite Relay kit in the list of items needed to tow late-model Ford trucks. However, with my 2023 F-150 XLT (push button start), it is simply impossible to install. The new Ford trucks do not even have a brake switch on the pedal and there is no visible wiring under the dash. I called Roadmaster, who immediately confirmed that they were aware of the issue. THE RELAY SWITCH IS NOT AN OPTION FOR 2021 AND NEWER F-150's. The only way to overcome the brake light override issue is to wait for the truck to enter "sleep mode." This occurs when you remove the key and don't open the door for 15 minutes. After that, the truck's electronics (body control module" shut off. Then the brake pedal can be pressed and the lights do not illuminate. Thus no relay is needed, you just have to wait 15 minutes. The motorhome wiring harness will work normally through the truck's tail lights, assuming you have installed the smart diode wiring kit for variable voltage. This part works great.
Installed as directions said to and all things are working as they should be. Helpful installation guide and video from trailer
Self installed, and easy to do if you just follow the videos and read the instructions. Quality hardware and fully functional after a full year of use. Jeep JK
Michael
4/19/2025
After a year and many miles towing all lights and hardware are functioning like the day they were installed. Etrailer, keep supplying quality products and techs providing video installation steps.
Installed as part of the InvisiBrake system. Since the InvisiBrake works, the relay kit must be performing its function.
Easy install, works great in my ‘04 TJ Rubicon and with a Ready Brake Tow Bar. I never think about it- just hitch up, plug in and go.
Installing on 2020 Jeep Trailhawk :
Pic #0557 : Roadmaster Base Plate Kit , Demco Supplemental Braking System , Diode Wiring Kit , Demco Battery Charge Wire Kit
Pic # 0548 ,0551 , 0559 Had to adjust the bracket plate to line up with the upper bolt holes
Pic #6028 finished install , mounted the operating unit to the top fuse box cover using automotive Velcro . Air cylinder , controller and LED light installed . Aside from the base plate bracket not lining up with the upper bolt holes I would give it 4 stars . My son in law is a master at solving mechanical issues .
The video help was priceless…just watch and follow step by step instructions for easy installation! After a year of use it has performed flawlessly, very pleased.
The “kit” is way over priced for what you get. The wire for the ignition connection is way too short to be useful. I could have bought all the parts at an auto store or Amazon for under $20.00.
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.
Richard
10/24/2018
Working great with no problems.
Brake light has worked perfectly. No issues. Very reassuring for me as the driver to be able to see in the Motorhome's rearview camera when the F150 is braking.
Great product but not required with the blue ox harness or the Hopkins harness
Delivered on time and in great condition. All components seem to be in the package.
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.
Well, if you don’t know about etrailer and you are into Towing or camping. You are missing the boat. This is the go to place and they have experts to guide you through the process of making sure that you find the right parts. I have purchased many things through the years from each trailer and could not be more pleased.
Basically part of a homemade wiring harness for a '79 Super Beetle. Can't say enough about our specialist at eTrailer--Kelsey knew her parts!
I really don't know. Due to health issues I sold the RV. Never used the tow bar. I'll try to sell it.
Clear instructions and an easy install. Worked great for keeping toad lights operating correctly with supplimental breaking system. Thanks for quick shipping!
My E-trailer experience was outstanding! From the great selection guide to the delivery to the installation support. The installation videos were very helpful. I had two installation issues that were answered with a prompt phone call. One call was on a Saturday morning. I highly recommend E-trailer!
Pulled entire length of route 66 and then some. We had absolutely no issues with all of our etrailer equipment. Thanks for all of your help.
2014 Honda CRV Brake switch relay. -Roadmaster 88400
Relay switch are really simple to install, but the location of the brake switch and the small wires made it really difficult.
But it works as it should
Didn’t need
Not required on a 2023 F-150 Platinum. E-trailer should have done better with their homework.
Great product
Info for this part was:
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Keith C.
5/3/2025
It worked great until I sold the vehicle. Used eTrailer to set up my new vehicle