How to Add a Third Brake Light to a Trailer

Updated 07/16/2024 | Published 12/29/2015

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Question:

I have a 2012 Honda Ridgeline with a factory 7 way plug. I have a trailer that Id like to add a single LED stop warning light. Many years ago I worked in the RV field and understand vehicle and trailer wiring very well. If the tow vehicle had separate stop lights, the four way connector would not work the stop on trailer as they worked through the turn signals. We put an adapter on the tow vehicle to make the four way work which I am sure you know. The only way I know is to use a flat or round 5 , 6, or 7 way and find the wire on the tow vehicle from the stop switch to the rear stop warning light. Not sure where in the harness his would be but sure it could be found. Add this wire to an empty terminal as the utility trailer does not have brakes or back up lights. On the trailer, run a wire from the stop warning light to a new connector. I saw a new stop warning light and it had three wire- ground and I think both turn signals. This makes sense as the stop light could be on while a turn is simultaneously being indicated. This is a simple connection please explain this electronic logic. Is there something inside the light that controls the signals., or is it just a miracle? Love your site

asked by: George M

Helpful Expert Reply:

To add a third brake light to a trailer is pretty simple, but does require an adapter to convert the signal.

Because trailer tail light systems combine the stop lamp and turn signals for each side onto a single circuit, you will need to use a vehicle-to-vehicle tail light converter, part # 118158 to split the brake light circuit back out.

The white wire on the input side of the converter would ground to the trailer frame, the green input wire would tap into the right turn circuit on the trailer and the yellow input wire would tap into the left turn circuit. For quick splices you could use the part # SWC501746-1. The output side of the converter also has three wires. The yellow and green wires are not needed for this application, and could be cut short and should be capped off. The red wire would connect to your third stoplight, with the light also grounded to metal on the trailer frame.

Looking at the diagram I produced for you will give you a good idea of the wiring layout.

expert reply by: Jameson C

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Andrew

7/14/2024

This solution warns that it will not work with LED lights. I have a nucamp T@G trailer that I want to add a brake warning light. Can I use this? Is yes, do you have a visual layout of the needed diodes?