Testing the Trailer Wires for Function Using a Circuit Tester on a Horse Trailer

Question:

I have a horse trailer that has no green wire the colors that it does have are Brown, Red, Blue, yellow, White it appears that the blue wire is grounded to the gooseneck? The yellow runs down to the left turn signal and the brown seems to run down to the right. White appears to be power for running lights. Red appears to be brakes. I am so confused!! I think it is a 80s kiefer goosneck trailer

asked by: Harry

Expert Reply:

My suggestion is to test the wires for function with the trailer connected to the tow vehicle. You will need a circuit tester, like # PTW2993, or a multimeter if you have one. You can start with any function, but I recommend starting with the left turn signal. It would help to have someone sit in the tow vehicle and engage the functions while you test the wires on the trailer.

With the left blinker on, probe the wires until you find the one that carries a signal in unison with the left signal. Next, do the same for the brakes, running lights, and right signal. The remaining wire will be the ground.

If would be beneficial and help with troubleshooting in the future to rewire the trailer in the most common method. A 5-wire system is: Green = right turn/brake, Yellow = left turn/brake, White = ground, Brown = running lights, Blue = electric brakes.

A 6-wire system is: Green = right turn/brake, Yellow = left turn/brake, White = ground, Brown = running lights, Blue = electric brakes, Red or black = battery. I have included a link to a wiring FAQ that explains the functions, wire colors, and size wire used on various connectors.

expert reply by: Michael H