Cargo Lamps
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The cargo lamp is controlled by the courtesy lamp supply voltage circuit. When the dimmer switch is turned clockwise to the farthest setting, the BCM recieves an input from the dimmer switch for courtesy lamps and cargo lamp to be commanded ON.