2003 GMC Sierra 1500 Pickup Owner's Manual - Page 369

When You Are Ready to Leave After Parking on a Hill 1. Apply your regular brakes and hold the pedal down while you: Trailer Wiring Harness Your vehicle is equipped with one of the following wiring harnesses for towing a trailer or hauling a slide-in camper. start your engine, shift into a gear, and release the parking brake. 2. Let up on the brake pedal. Basic Trailer Wiring All regular, extended cab crew cab pickups have a six-wire trailer towing harness. 3. Drive slowly until the trailer is clear of the chocks. 4. Stop and have someone pick up and store the chocks. Maintenance When Trailer Towing Your vehicle will need service more often when you're pulling a trailer. See the Maintenance Schedule for more on this. Things that are especially important in trailer operation are automatic transmission fluid (don't overfill), engine oil, axle lubricant, belt, cooling system and brake system. Each of these is covered in this manual, and the index will help you find them quickly. If you're trailering, it's a good idea to review these sections before you start your trip. Check periodically to see that all hitch nuts and bolts are tight. 4-88 The six-wire harness is located at the rear of the vehicle and is tiedto the vehicle's frame. The harness requires the installation of a trailer-wiring harness connector, which is available through your dealer.