Only Brake Lights are Working on Trailer with All New Lights

Updated 11/03/2017 | Published 11/02/2017

Question:

My lights on my trailer are all new. They only work when the brakes are pressed. Also if the headlights are on they wont work at all. Please help.

asked by: Aaron

Expert Reply:

It sounds like a short, ground problem, or wiring issue. There are some things you can check to determine where the issue is.

First, disconnect the trailer from the tow vehicle. Then make sure that the vehicle side trailer connector is clean and free of corrosion inside, where the wires attach (if possible) and outside on the pins. Corrosion can interrupt the transfer of electricity from the tow vehicle to the trailer.

Next, use a circuit tester such as # PTW2993 or a meter if you have one to test the pins on the vehicle side connector. Have someone sit in the vehicle and operate the light functions while you test. If none of the pins have power when the turn signals are activated or when the running lights are on, then there is a problem on the vehicle side; potentially a miswired connector or blown or missing fuses or relays (on vehicles with a factory tow package).

If everything is working as it should on the vehicle side, then the issue must be on the trailer. Check the trailer connector for corrosion too. You can trace the wiring from front to back and fix and damaged or pinched wires.

If it is a ground issue, then 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 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.

I have included links to a couple of help articles that may also help.