GMC 1999 Sierra 1500 Pickup Owner's Manual page 236

Your Driving and the Road
Total Weight on Your Vehicle's Tires
Be sure your vehicle's tires are inflated to the limit for cold tires. You'll find
these numbers on the Certification label at the rear edge of the driver's door
(or see "Tire Loading" in the Index). Then be sure you don't go over the
GVW limit for your vehicle.
Hitches
It's important to have the correct hitch equipment. Crosswinds, large trucks
going by, and rough roads are a few reasons why you'll need the right hitch.
Here are some rules to follow:
If your vehicle has a step bumper and you are going to use a ball-type
hitch, remove the pad and cut holes in it to match the hitch and safety
chain holes in the bumper.
If you'll be pulling a trailer that, when loaded, will weigh more than 4,000
pounds (1800 kg) be sure to use a properly mounted weight-distributing
hitch and sway control of the proper size. This equipment is very
important for proper vehicle loading and good handling when you're
driving.
Safety Chains
You should always attach chains between your vehicle and your trailer. Cross
the safety chains under the tongue of the trailer so that the tongue will not
drop to the road if it becomes separated from the hitch. Instructions about
safety chains may be provided by the hitch manufacturer or by the trailer
manufacturer. Follow the manufacturer's recommendation for attaching safety
chains. Always leave just enough slack so you can turn with your rig. And,
never allow safety chains to drag .on the ground.
Trailer Brakes
If your trailer weighs more than 1,000 pounds (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.
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 ~ ~ ) of fluid from your vehicles master cylinder.
If it does, both braking systems won't work well. You could even lose your
brakes.
Will the trailer brake parts take 3,000 psi (20 650 kPa) of pressure? If
not, the trailer brake system must not be used with your vehicle.
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.
If
you do, it will bend and finally break
off.
Use steel brake tubing.
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