Inside Rear View Mirror Lamp
WARNING: This page is about a different car, the 2002 Oldsmobile Intrigue. However, it is still accessible from the selected car via links, so may be relevant.
The inside rear view mirror lamp is turned ON by the dimmer switch, the inside rear view mirror switch, or during illuminated entry.
During illuminated entry or when the dimmer switch is ON the body control module (BCM) wakes up and then energizes the courtesy lamps supply voltage circuit, suppling voltage to all interior lamps. The BCM pulls the interior lamp control circuit low, providing ground to the inside rear view mirror lamp and all courtesy lamps.
The inside rear view mirror lamp can be turned on from the inside rear view mirror switch. The BCM supplies voltage through the courtesy lamps supply voltage circuit when the BCM is awake. Manually turning on the inside rear view mirror switch provides a ground path.