GMC 2007 Yukon XL Owner's Manual page 415

Safety Chains
You should always attach safety chains between
your vehicle and your trailer. Cross the safety
chains under the tongue of the trailer to help
prevent the tongue from contacting the road if it
becomes separated from the hitch.
Attach the safety chains to the attaching point on
the hitch platform. If you are towing with an
aftermarket hitch, following the trailer or hitch
manufacturer's recommendation for attaching
safety chains. Always leave just enough slack so
you can turn with your rig. Never allow safety
chains to drag on the ground.
Trailer Brakes
If your trailer weighs more than 2,000 lbs (900 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.
If your vehicle is equipped with StabiliTrak
your trailer cannot tap into the vehicle's hydraulic
brake system.
Your trailer brake system can tap into the vehicle's
hydraulic brake system only if:
•
The trailer parts can withstand
3,000 psi (20 650 kPa) of pressure.
•
The trailer's brake system will use less than
0.02 cubic inches (0.3 cc) of fluid from your
vehicle's master cylinder. Otherwise, both
braking systems won't work well. You could
even lose your brakes.
If everything checks out this far, make the brake tap
at the port on the master cylinder that sends the
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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