Trailer Turn Signals and Running Lights Work Until Brakes are Applied and Brake Lights Never Work

Question:

The running lights and turn signals work on the trailer. When I press the breaks all the lights on the trailer shut off. The break lights will not come on when applied at all with or without the running lights on. Where should I start looking for issues

asked by: R M

Expert Reply:

This sounds like a ground issue and/or a possible short. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H