Trailer Lights Do Not Light Up But have Power on All Wires

Updated 09/19/2024 | Published 10/26/2015

Question:

I hooked up a 12 volt car battery to work the trailer lights.. Used a test light and I have power in all the trailer plug wires at the same time, but no lights on the trailer. Why do all the wires have power in them at the same time , and no lights ?

asked by: Mike A

Expert Reply:

The problem you are experiencing sounds like a ground issue and/or short circuit. 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. I have also included a couple of help articles for you.

expert reply by: Michael H

Jax

9/19/2024

I am having the same issue as this user, but the trailer lights are working just fine when plugged into a different truck/tow vehicle. Test light shows I am getting correct power to tow harness, but trailer lights only work about 10% of the time. Almost seems like there isn't enough voltage getting through the system.