I/P Courtesy Lamp
WARNING: This page is about a different car, the 2004 Buick Regal and 2004 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The I/P courtesy lamp is turned ON by the I/P dimmer switch or during illuminated entry.
During illuminated entry or when the I/P dimmer switch is ON the BCM wakes up and then energizes the courtesy lamps supply voltage circuit, suppling voltage to all interior lamps. The BCM pulls the courtesy lamp low control circuit low, providing ground to the I/P courtesy lamps and all courtesy lamps.