1999 GMC Envoy Owner's Manual - Page 218

yellowblue 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. D Red: Use for battery charging; it connects to the starter solenoid. D D D D D D Light Green: Back-up lamps. Brown: Taillamps and parking lamps. Yellow: Left stoplamp and turn signal. Dark Green: Right stoplamp and turn signal. White (Heavy Gauge): Ground wire. White (Light Gauge): Auxiliary stoplamp. Trailer Wiring Harness The heavy-duty trailer wiring is an eight-wire harness assembly. The harness is stored under the vehicle, on the driver's side corner frame rear crossmember. The heavy-duty trailer wiring has a 30-amp feed wire with an in-line fuse located by the junction block. See "Fuses and Circuit Breakers" in the Index. The harness does not have a connector and should be wired by a qualified electrical technician. The technician can use the following color code chart when connecting the wiring harness to your trailer. Securely attach the harness to the trailer, then tape or strap it to your vehicle's frame rail. Be sure you leave it loose enough so the wiring doesn't bend or break, but not so loose that it drags on the ground. Store the harness in its original place. Wrap the harness together and tie it neatly so it won't be damaged. D Dark Blue: Use for electric trailer brakes or auxiliary wiring. 4-54