Troubleshooting Trailer Running Lights Not Working, Turn Signals and Brake Lights Do Work

Question:

all my lights on the trailer work except running lights. i have a disconnected white wire on my 5-way going to the trailer, i cant tell where it goes.

asked by: Philip T

Expert Reply:

The white wire is probably the ground wire, and it needs to be connected to a clean, corrosion free bare metal surface on the trailer frame. Without a good ground, some or all of the trailer lights will not work or work properly.

You can also check the grounds for each taillight. Trailer taillights usually ground through the mounting studs and they, too, will need to be attached to a clean corrosion free bare metal surface.

There is not always a universal wiring color code that everyone follows, so there is a chance that the white wire on your trailer is being used for the running lights. You can test the corresponding pin on the vehicle side connector using circuit tester # PTW2993 to determine if it is carrying the running light circuit. However, this does not guarantee that the trailer and vehicle connectors are pinned out the same.

expert reply by: Michael H