4 Pole Trailer Connector Wire Color Code

Question:

My plug has 4 wires red brown green and yellow Iwhich one is the ground wire

asked by: Robert

Expert Reply:

Is this for the connector on the trailer or the vehicle?

If it's on the vehicle, use a circuit tester like # PTW2993 on each wire as a helper activates the taillight functions. The yellow is typically left turn/brake lamp, the green is usually right turn/brake lamp, and the brown usually carries the running lamp circuit. Ground the tester to the vehicle and have your helper turn on each taillight function one at a time as you test each wire. Chances are the red wire is the ground.

If you're talking about the connector on the trailer itself, look for the main trailer ground on the trailer tongue and see which color wire is grounded. You can use a car battery to apply 12V to the other three wires to confirm their function by seeing which taillight circuit is activated when power is applied.

expert reply by: Mike L