GM Service Manual Online
For 1990-2009 cars only

Heavy-Duty Trailer Wiring Package

The vehicle may be equipped with an eight-wire trailer towing harness. This harness, with a seven-pin universal heavy-duty trailer connector, is attached to a bracket on the platform hitch.

The Center High-Mounted Stoplamp (CHMSL) wire is tied next to the trailer wiring harness for use with a trailer.

The eight-wire harness contains the following trailer circuits:

    • Yellow: Left Stop/Turn Signal
    • Dark Green: Right Stop/Turn Signal
    • Brown: Taillamps
    • White: Ground
    • Light Green: Back-up Lamps
    • Light Blue: CHMSL
    • Red: Battery Feed
    • Dark Blue: Trailer Brake

Trailer Connections (C7/C8 Models Only)

If the vehicle has these trailer connections, they are located at the rear of the cab for a tractor and at the rear of the chassis when towing a trailer. There will be an air connection and an electrical connection.

Be sure that the couplings to the trailer are made correctly.

Air Connections

If the trailer air line connections will not be connected to another piece of equipment, be sure to replace their protective caps.

Electrical Connections

This system is a seven-wire cable that will connect to the trailer, supplying power to the trailer's lighting system. When not in use, it is stored in the trailer air-hose storage bracket.