How to Re-Wire Trailer with 4-Pole Trailer Harness

Question:

My trailer is wired with 3 wire plus an external ground which has a black,greenand white wires , trying to wire to a 4 wire plug which has green brown yellow and a white , having no luck.

asked by: Brian

Expert Reply:

A 4-pole trailer wiring harness has three circuits plus a ground, the ground being carried on the white wire. You will just need to test the functions on each trailer wire to confirm how to connect them to a 4-pole pigtail like # HM38138. A junction box # 38656 and ring terminals like # 44-5310A will make it easier to get solid reliable connections.

You will want to ground a battery negative terminal to the frame and apply 12V power from the positive terminal to each trailer circuit, one at a time, to see what lights operate. Once you know what each trailer wire does you can follow the wiring guide in the linked article to help you make the correct splices to the 4-pole.

On standard 4-pole wiring the white wire is ground, the brown wire is running lights and the green and yellow wires carry right stop/turn and left stop/turn signals, respectively.

expert reply by: Adam R