Air Connections; Electrical Connections - GMC 2003 C4C042 Owner's Manual

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The eight wire harness contains the following
trailer circuits:
D
Yellow: Left Stop/Turn Signal
D
Dark Green: Right Stop/Turn Signal
D
Brown: Taillamps
D
White: Ground
D
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Light Green: Back up Lamps
D
Light Blue: CHMSL
D
Red: Battery Feed
D
Dark Blue: Trailer Brake
Trailer Connections (C6/C7/C8
Models Only) (If Equipped)
If your 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 you are not connecting the trailer air line connections
to another piece of equipment, be sure to replace their
protective caps.

Electrical Connections

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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
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air hose storage bracket.
NOTICE:
Starting in 1998, the center pin (also known as
the auxiliary circuit) of the seven
electrical connector will be wired to provide
continuous power for the trailer anti
systems when the ignition key is in the on
position. Care should be taken to insure that
continuous power on this circuit will not cause
damage to the trailer electrical system.
Consult with the trailer manufacturer for the
proper operation and checking procedures for
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the trailer anti lock brake systems.
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pin trailer
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lock brake
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