How to Test to Determine Vehicle Wiring Function on 2004 Duramax 2500

Updated 07/12/2017 | Published 07/10/2017

Question:

The wiring colors red , white , blue are larger wires. Then others smaller: brn, green, yellow, very pale green. I am trying to wire the female plug on the p/u , please help if you can inform me. Thanks

asked by: Scott D

Helpful Expert Reply:

With a vehicle 7-way wiring harness usually the larger-gauge wires are used for ground (usually white), 12V auxiliary power (often red or black) and the trailer brake circuit (usually a blue wire).

As for the other wire colors, these are typically brown for running lights, green for right stop/turn, yellow for left stop/turn. The other wire, in your case a pale green one, would typically carry the reverse light signal.

But wire colors are not always a reliable method to determine the functions carried on them so testing to find the wire function is the best way to go. A circuit tester like # PTW2993 makes it easy to determine which signal is on which wire. Just have a helper sit in the vehicle and activate the lighting functions, one at a time, while you test the wires. Please refer to the linked video.

You can also refer to the linked article for help on vehicle/trailer wiring configurations.

expert reply by: Adam R