Chevrolet 2003 Silverado Owner's Manual page 374

If your vehicle is equipped with the "Heavy-Duty
Trailering" option, please refer to Heavy-Duty Trailer
Wiring Package , earlier in this section.
When the camper-wiring harness is ordered without the
heavy-duty trailering package, an eight-wire harness
with a seven-pin connector and separate CHMSL
connector are located at the rear of the vehicle and are
tied to the vehicle's frame.
4-92
Instrument Panel Jumper Wiring Harness
This harness may be included with your vehicle as part
of the heavy-duty trailer wiring package.
This harness is for an electric brake controller and
includes a trailer battery feed fuse. It should be installed
by your dealer or a qualified service center.