Trailer Brake Hand Control Valve; Rear Axle Differential Lock Control - GMC 2010 T-Series Owner's Manual

Trailer Brake Hand Control Valve

If your vehicle has this feature, the control is mounted
on the floor console.
You can apply the trailer brakes a little or apply them all
the way if you have to. Use this control only when you
are driving. Do not use it for parking or to hold the rig
on a hill.
4-6
This feature lets you apply
the trailer brakes without
applying the tractor
brakes.
WARNING:
Using the trailer brake hand control for parking or
for holding the vehicle on a hill may not keep the
vehicle from rolling. This can happen if someone
hits the valve by accident, or if air pressure bleeds
from the system. If the vehicle rolls, you or others
could be injured. To park the vehicle or hold it on
a hill, use the parking brake properly.

Rear Axle Differential Lock Control

This control is on single rear axle vehicles.
If the vehicle has a
controlled traction or
locking differential axle,
the switch is located in
the center of the
instrument panel.