With Vehicle Head Lights On Trailer Turn and Brake Lights Do Not Work

Question:

When the head lights are on the right side of the trailers turn and brake lights arent working. Otherwise they work. Just trying to see what might be causeing that to happen, and any advice on how to fix the problem?

asked by: Shawn

Expert Reply:

The problem you are having is indicative of a bad ground connection. Ground issues usually show up when there is more load on the system. In this case the constant draw of the running lights is causing too much power draw for the weak ground when you try to use another function.

Make sure that the main trailer connector ground and the grounds for all of the lights are attached to clean and corrosion free bare metal surface. Anything placed between a ground wire and the metal frame can interrupt the ground.

Trailers with an aluminum frame, folding tongue, or tilt bed can also have this problem. You would need to run jumper grounds from the light grounds to the main trailer connector ground.

It is also possible that the power draw from the trailer exceeds what the vehicle can handle. If you have OEM trailer wiring on the vehicle then check the owners manual or a dealership to see how much the system is rated for. Then compare that to the power draw from the lights. The power draw for each light should be listed somewhere on the light.

If you have aftermarket wiring, the amperage rating should be on the converter box (if equipped) or, if it draws power through the tail light wiring on the vehicle you would need to know what the vehicle tail lights are rated for. Since you are using LED trailer lights I doubt it is a power draw problem.

expert reply by: Michael H