How Can I Identify the Power and Ground Wires on my Trailer with a 7-Way Plug

Question:

I have a 16 foot trailer with a 7 way plug and doesnt have a white wire for the ground the colors it has is black ,blue, red, yellow, green, brown which one would be the ground on the plug

asked by: Danny M

Expert Reply:

With out being there to test it it is hard to tell you. We can eliminate some stuff though. Generally the yellow is left turn and brake, green is right turn and brake, brown is running lights, blue is brake signal. This leaves you with black and red. If I had to guess black would be ground and red would be 12 volt power but this could also be backwards.

If you'll use a test light like the Hook Probe Circuit Tester part # PTW2993. Hook the clamp to a clean part of the trailers steel and test each one the one that lights up is 12 volt power the one that doesn't is ground. This test should be done while connected to the vehicle with the ignition on to ensure power is being sent.

expert reply by: Randy B