Utility Trailer Lights Work when Vehicle is Off But Stop Working When Vehicle is On and Running

Updated 08/01/2014 | Published 07/31/2014

Question:

when I plug my trailer to my car and my engine is off the trailer lights work but when I turn my ignition on and my lights are on they stopped working

asked by: Bry

Expert Reply:

There could be a problem inside the vehicle or trailer side connector. You will need to make sure that each is clean and corrosion free inside and out. If your vehicle has a 12 volt circuit at the trailer connector that is only one when the truck is on, and it is shorting out due to corrosion, that could be the cause of the problem.

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. Or anything that creates more load, perhaps even with the vehicle is on.

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