Manual Interior Lighting
WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
The interior lamps may also be illuminated manually in all ambient light conditions. When a vehicle occupant places the driver information center (DIC)/dimmer switch to the interior lamp ON position, the contacts in the switch close grounding the interior lamp input circuit of the instrument panel module (IPM). With this input grounded, the IPM sends a GMLAN serial data message to the RIM requesting the interior lamps illuminate. The RIM will ground the lamps as mentioned above. When the I/P dimmer switch is placed out of the interior lamp ON position, the RIM will immediately turn OFF the interior lamps.