GMC Sierra Classic 2007 Owner's Manual page 456

Auxiliary Battery
The auxiliary battery provision can be used to
supply electrical power to additional equipment that
you may choose to add, such as a slide-in
camper.
When using this provision, connection should only
be made to the upper stud (A) of the relay. Do not
make connections to the lower stud (B) of the relay.
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If your vehicle has this
provision, this relay will
be located on the
passenger's side of the
vehicle, next to the
auxiliary battery.
The auxiliary battery circuit is protected by a
megafuse located behind the auxiliary battery.
Be sure to follow the proper installation instructions
that are included with any electrical equipment
that you install.
Notice: Leaving electrical equipment on for
extended periods will drain the battery. Always
turn off electrical equipment when not in
use and do not use equipment that exceeds
the maximum amperage rating for the auxiliary
battery provision.
Power Winches
If you wish to use a power winch on your vehicle,
only use it when your vehicle is stationary or
anchored.