Roof Rail Courtesy Lamps
WARNING: This page is about a different car, the 2003 Buick Regal and 2003 Buick Century. 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 IP dimmer switch, the individual roof rail courtesy lamp switch, or during illuminated entry.
During illuminated entry or when the IP 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 roof rail courtesy lamps and all courtesy lamps.
The roof rail courtesy 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.