Trailer Light Wire Functions and Installing a 4-Way Harness on a Trailer

Question:

hi i have a small trailer that only has three wires for the lights and i want to put on a four flat trailer adapter the colors from the trailer lights are black white and green.could u tell me how this conects .do i have to double somthing up?

asked by: Joe

Expert Reply:

Trailer lights have combined brake and turn signal circuits, a running light circuit, and a ground. Most likely, the black wire on your light is for the running lights, green is for stop and turn, and white is ground. Use a circuit tester like # 3808 if needed to confirm the wire functions.

On a harness like # 18004, you will need to have a jumper wire (basically split) the brown running light circuit to go to each side of the trailer. The other option is to use a wishbone harness, # A35W42B. This harness has the running light circuit split at the connector so you do not need to split the running light circuit. I have included a link to a video showing a typical installation.

expert reply by: Michael H