GMC 2012 Sierra Denali Owner's Manual page 320

These wiring provisions are
included with the vehicle as part of
the trailer wiring package. These
provisions are for an electric brake
controller. The instrument panel
contains blunt cut wires near the
data link connector for the trailer
brake controller. The harness
contains the following wires:
Dark Blue: Brake Signal to
Trailer Connector
Red/Black: Battery
Light Blue/White: Brake Switch
White: Ground
The harness should be installed by
your dealer or a qualified service
center.
If the vehicle is equipped with an
Integrated Trailer Brake Control
(ITBC) System, the blunt cuts exist,
but are not connected further in the
harness. If an aftermarket trailer
brake controller is installed, the
ITBC must be disconnected. Do not
power both ITBC and aftermarket
controllers to control the trailer
brakes at the same time.
Pressing this button at the end of
the shift lever turns on and off the
Tow/Haul Mode.
This indicator light on the instrument
panel cluster comes on when the
Tow/Haul Mode is on.
Tow/Haul is a feature that assists
when pulling a heavy trailer or a
large or heavy load. See
for more
information.
Tow/Haul is designed to be most
effective when the vehicle and
trailer combined weight is at least
75 percent of the vehicle's Gross
Combined Weight Rating (GCWR).
See Weight of the Trailer in
. Tow/Haul is
most useful under the following
driving conditions:
When pulling a heavy trailer or a
large or heavy load through
rolling terrain.
When pulling a heavy trailer or a
large or heavy load in
stop-and-go traffic.
When pulling a heavy trailer or a
large or heavy load in busy
parking lots where improved low
speed control of the vehicle is
desired.