7-Way Wire Color Functions for Adapter 4 Pole to 7 Pole Vehicle End Trailer Connector, # 30717

Expert Reply:

You are correct. The white wire is grounded to the frame, the black wire runs to the battery, and the blue wire is run to your trailer brake controller. The yellow wire is an auxiliary wire, and can be used for whatever extra purpose you need it for. If you have reverse lights on your trailer or hydraulic surge brakes with reverse lockout, you can splice the yellow wire into your vehicle reverse lights or to the lockout. I have posted links to our wiring help pages for you to review.

expert reply by: Andi