Chevrolet 2003 Silverado 1500 Pickup Owner's Manual page 370

The six-wire harness contains the following trailer
circuits:
0
Yellow: Left Stop/Turn Signal
Dark Green: Right Stopnurn Signal
Brown: Taillamps
0
White: Ground
Light Green: Back-up Lamps
Light Blue: Center High-Mounted Stoplamp
(CHMSL)
If you need to upgrade your trailer wiring harness, an
additional 2-wire harness and 7 pin universal trailer
connector are available from your dealer.
Trailer Wiring Harness Package
~ ~~~~ ~
tour pickup may be equipped with the eight-wire trailer
\
towing harness. This harness with a seven-pin
universal trailer connector is attached to a bracket on
the hitch platform.*
*
The Center High-Mounted Stoplamp (CHMSL) wire is
tied next to the trailer wiring harness for use with a
trailer, slide-in camper or cap.
4-89