2003 GMC Sierra 1500 Pickup Owner's Manual - Page 372

A If your vehicle has this provision, this relay will be located on the passenger's side of the vehicle, next to the auxiliary battery. If your vehicle is equipped with the "Heavy-Duty Trailering" option, please refer to Heavy-Duty Trailer Wiring Package, earlier in this section. When using this provision, connection should only be made to the upper stud (A) of the relay. Do not make connections to the lower stud (B) of the relay. The auxiliary battery circuit is protected by a megafuse located behind the auxiliary battery. Be sure to follow the proper installation instructions that are included with any electrical equipment that you install. Notice: When using the auxiliary battery provision, the electrical load must not exceed 30 amps. Always turn off any electrical equipment when not in use. Leaving electrical equipment on for extended periods will drain your battery. 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. Auxiliary Battery The auxiliary battery provision can be used to supply electrical power to additional equipment that you may choose to add, such as a slide-in camper. 4-9 1