1996 GMC Safari Owner's Manual - Page 187

Trailer Brakes If your trailer weighs more than 1,000 lbs. (450 kg) loaded, then it needs its own brakes -- and they must be adequate. Be sure to read and follow the instructions for the trailer brakes so you'll be able to install, adjust and maintain them properly. Your trailer brake system can tap into your vehicle's hydraulic brake system, except: Don't tap into your vehicle's brake system if the trailer's brake system will use more than 0.02 cubic inch (0.3 cc) of fluid from your vehicle's master cylinder. If it does, both braking systems won't work well. You could even lose your brakes. 0 Driving with a Trailer I If you have a rear-most window open andyou pull a trailer with your vehicle, carbon monoxide (CO) could come into your vehicle. You can't see or smell CO. It can cause unconsciousness or death. (See "Engine Exhaust" in the Index.) To a maximize your safety when towingtrailer: 0 Have your exhaust system inspected for leaks, and make necessary repairs before starting on your trip. Keep the rear-most windows closed. 0 If exhaust does come intoyour vehicle through a window in the rear or another opening, drive with your front, main heating or cooling system onand with the fan on any speed. This bring fresh, will outside air into your vehicle. Do not use MAX A/C because it only recirculates the air inside your vehicle. (See "Comfort Controls" in the Index.) Will the trailer parts take 3,000 psi (20 650 kPa) of pressure'?If not, the trailer brake system must not be used with your vehicle. 0 If everything checks out this far, then make the brake fluid tap at the port on the master cylinder that sends fluid to the rear brakes. But don't use copper tubing for this. I f you do, it will bend and finally break off. Use steel brake tubing. 4-33