Troubleshooting Trailer Tail Light Wiring

Updated 09/04/2018 | Published 09/02/2018

Question:

I have 3 wires on the lights on one 2 green 1purple the other 2 yellow 1 purple on the harness is one side brown one green the other side one yellow one green plus the white wire what goes were

asked by: Tim

Expert Reply:

With 3 wires on tail lights, you normally will have one running light wire, one brake light/turn signal wire and a ground wire. You are most likely correct that the two identical color wires will be one for running lights. The purple wire could be a separate ground, or if you have reverse lights will be the reverse light wire. If that is the reverse light, then the tail lights will ground through the mounting hardware so will want to make sure you have a solid metal to metal connection free of debris or corrosion.

The best way to test the wiring function of your lights is to simply connect a 12V battery to each wire to test it. If your tail lights have no white or clear lens then your purple wire is most likely the ground. If it does have a white or clear lens then you will connect the ground to your mounting screws to test functions.

expert reply by: Jason S