GMC 2010 Sierra 1500 Crew Cab Owner's Manual page 242

To use an accessory power outlet, remove the
protective cap. When not in use, always cover the
accessory power outlet with the protective cap.
Certain power accessory plugs may not be compatible
to the accessory power outlet and could result in blown
vehicle or adapter fuses. If you experience a problem,
see your dealer for additional information on the
accessory power plugs.
The accessory power outlets are powered, even when
the ignition is in LOCK/OFF. Continuing to use power
outlets while the ignition is in LOCK/OFF may cause the
vehicle's battery to run down.
4-18
When adding electrical equipment, be sure to follow the
proper installation instructions included with the
equipment.