GMC Sierra Denali Classic 2007 Owner's Manual page 318

The eight-wire harness contains the following
trailer circuits:
•
Yellow: Left Stop/Turn Signal
•
Dark Green: Right Stop/Turn Signal
•
Brown: Taillamps
•
White: Ground
•
Light Green: Back-up Lamps
•
Light Blue: Center High-Mounted
Stoplamp (CHMSL)
•
Red: Battery Feed**
•
Dark Blue: Trailer Brake
**If you are charging a remote (non-vehicle)
battery, press the tow/haul mode button located at
the end of the shift lever. This will boost the
vehicle system voltage and properly charge the
battery. If the trailer is too light for tow/haul mode,
you can turn on the headlamps as a second
way to boost the vehicle system voltage and
charge the battery.
318
Electric Brake Control Jumper
CAUTION:
{
Be sure to use only the correct trailer
brake harness, the one intended for use
on your vehicle. If you use some other
trailer brake harness, even if it seems to
fit, your trailer brakes may not work at all.
You could have a crash in which you or
others could be injured. Use only the
trailer brake harness intended for your
vehicle. If it is no longer available to you,
be sure to get a proper replacement from
your dealer.