1994 GMC Suburban Owner's Manual - Page 136

If you need to carry long items, move the cross rails as far apart as they will go. Tie the load to the cross rails and the side rails or side rail supports. Also tie the load to the bumpers. Do not tie the load so tightly that the cross rails or siderails are damaged. After moving the cross rails, be sure to tighten all the slider screws. Trailer Wiring Harness (Option) An optional 7-wire harness is stored under your vehicle along the rear frame crossmember. The harness has a 30 amp. in-line fused battery feed wire and n o connector, and should be wired by a qualified electrical technician. 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 won't bind or break when turning with the trailer, but not so loose that it drags on the ground. Store the harness in its original position. Wrap the harness together and tie it neatly so it won't be damaged. 2-80