Trailer Lights Not Working Unless Truck Lights are Off and Brake Pedal is Pressed

Question:

None of the lights work on the trailer, if I shut my truck lights off and push on the breaks all the lights on the trailer come on but if I let off the breaks or turn my truck lights on I loose everything, they only work with breaks pushed an truck lights off. Trucks fine works on any other trailer

asked by: Dylan

Expert Reply:

Since the truck works with any other trailer just fine the issue must be on the trailer. Check its connector and make sure it is clean and free of corrosion inside where the wires attach and outside on the pins.

It could also be a ground issue. 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.

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