Trailer Lights are Dim When Connected to Truck

Updated 05/03/2017 | Published 05/01/2017

Question:

i have a 4 post plug on my tralior and truck with the test lite shows wired correctly but when i plug the them in the lites are dim and when you when you use the blinkers they both flash very dim and i cleaned the frame and made a new ground to the frame

asked by: Don D

Expert Reply:

Sounds like you have a ground issue on your trailer. 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.

Locate the main trailer ground wire. Disconnect the wire and clean the surface that the wire is connected on your trailer. Make sure that the connection is on bare metal. No rust, paint, dirt, or grease on the trailer's surface where the ground will be attaching.

Also, make sure the vehicle side and the trailer side connectors are free of corrosion both inside and out.

Check the light grounds to make sure they are attached to a clean and corrosion free bare metal surface. If there is anything in between the light grounds and the metal trailer frame could interrupt the ground.

The attached diagram will show the what the general wiring for a trailer.

expert reply by: Jared P