Rear Dome Lamp
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
Power comes from the dome fuse, through the left instrument panel junction block and finally to the rear dome lamp. When the rear tailgate is opened the rear compartment lamp switch closes providing a path to ground. With ground and power supplied the lamp will illuminate.