Right Brake Light Does Not Work But All Other Lights Do Work

Question:

When i hook up a new trailer thats been tested to my truck, the right turn works on the trailer but the right brake light will not work. Is it not on the same wiring function. The right stop and turn are the same fuse, any idea what the issue is.

asked by: Ryan F

Expert Reply:

Typically, because trailers use a combined system with brake lights and turn signals on the same circuit, when a turn signal works and the same side brake light does not, that is an indication of a ground problem. Basically, ground issues can appear when there is more load on a system. The brake light is a constant, bright light drawing power and can expose that weak ground.

The problem is finding the ground problem source. Start by disconnecting the trailer and making sure the vehicle and trailer side connectors are clean and free of corrosion inside and out. Then use a circuit tester such as # PTW2993 if you need one to test the truck side connector to make sure everything is functioning properly. If it is not, then check the tow package wiring, fuses, or relays.

On the trailer side you will need to make sure the main trailer connector ground is attached to a clean and corrosion free bare metal surface and do the same for each of the lights. If the trailer has an aluminum frame, tilt bed, or folding tongue, or if you added a license plate bracket between the light ground and trailer frame, those things can interrupt the ground. Running jumpers from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H