How to Install an Amber Turn and Parking Light on a Trailer with Combined Brake and Turn Signals

Question:

My trailer has a combined system with your basic 4 wire flat plug starting at the front I am wanting to mount MC32AB lights on the front of the fenders and use them as running lights and turn signals.I do not want them to light up when the brakes are applied. The rear of my trailer has combined tail lights. How can i go about wiring these in to work? .

asked by: David H

Expert Reply:

Many people inquire about wiring a trailer in the way you describe, and it is possible, but you will need to use a vehicle to vehicle taillight converter, part # 118158, to accomplish this. The converter will be wired inline on the trailer wiring and will break out the turn and brake circuits.

I attached a drawing that shows how I would go about wiring this converter on a simple 4 wire trailer. You would just need to cap off the red wire on the output side of the converter and tie that wire up out of the way, since you will not need to run it to the back of the trailer for brake light function.

When mounting the converter box you should try to mount it in an area that is protected from the elements as much as possible, to avoid moisture getting into the converter housing.

expert reply by: Robert G

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Rafael E.

12/9/2012

I have the same problem and this really helps. Now I am wondering if by any chance I could use a third break light bar and connect it as a running light and also turn on even brighter when I apply the breaks? Can I connect it with the brown wire and the red wire in the output of the converter for this to work?

Patrick B.

12/11/2012

You wire the lights that way. Follow the diagram on the answer from the original question. In order to have it function as both a running/clearance light and a brake light, you will need to make sure whatever light you choose has the ability to carry those functions, typically listed as a 3 function. Using the dedicated brake output line from the converter box will ensure that the light only brightens with the brakes and not the turns. Something like STL79RB should work well as a center tail/brake light, similar to what you would have on the top of a pickup cab.