Roof Rail Courtesy/Reading Lamps
WARNING: This page is about a different car, the 2006 Buick Lucerne. However, it is still accessible from the selected car via links, so may be relevant.
The roof rail courtesy lamps are turned ON by the lamp switch assembly, the individual roof rail courtesy lamp 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 roof rail courtesy/reading lamps can be turned ON from the individual roof rail courtesy lamp switch. The BCM supplies voltage through the courtesy lamps supply voltage circuit when the BCM is awake. Manually turning ON the roof rail courtesy lamp switch provides a ground path.