GMC 2001 Sierra - Manual (Page 302)

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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.
Instrument Panel Jumper Wiring Harness
This harness is included with the heavy - duty and
camper/fifth - wheel trailer wiring packages. The harness
is for an electric trailer brake controller and includes a
trailer battery feed fuse. This harness and fuse should be
installed by your dealer or a qualified service center.