How to Find Wire Functions for Trailer Wiring On a 2006 Ford Ranger

Expert Reply:

Since there is no standard for wire color and function, you would have to test the wires using a circuit tester such as # PTW2993 to determine their functions. One the trailer side it is likely that yellow is left turn/brake lights, green is right turn/brake lights, yellow/gray is running lights for the left side, and green/gray is running lights for the right side. White would be the ground.

But you will also want to test the trailer wires (if there is a connector on the trailer side already then testing is not necessary). You can either trace each wire back to see where they all terminate. Or you can use a separate 12-volt battery and apply power to each wire and see what turns on.