GMC Defense 2006 Owner's Manual Supplement page 54

To avoid the possibility of the vehicles rolling, set the
parking brake firmly on both vehicles involved in the
jump start procedure. Put the automatic transmission in
PARK (P). Be sure the transfer case is in a drive gear
and is NOT in NEUTRAL (N).
Notice: If you leave the communications/navigation
equipment or other accessories on during jump
starting procedure, they could be damaged.
The repairs wouldn't be covered by the warranty.
Always turn off your communications/navigation
equipment or other accessories when jump
starting your vehicle.
3. Turn off the ignition on both vehicles. Unplug
unnecessary accessories plugged into the
cigarette lighter or accessory power outlets. Turn
off all lamps that aren't needed as well as radios.
This will avoid sparks and help save both
batteries. In addition, it could save the radio!
4. Locate the slave
receptacles on both
vehicles and unscrew
the cover.
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