Interior Lighting System
WARNING: This page is about a different car, the 2008 Ford RV Cutaway, 2008 Ford Econoline, 2008 Ford E450 Super Duty, and 2008 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
The instrument cluster (IC) illuminates the interior lamps based on input signals from the door ajar switches, headlamp switch and the vehicle security module (VSM). The IC monitors the door ajar switch status on the input circuits for a ground supplied through the ajar switches indicating an open door. The IC then grounds the battery saver relay and the interior lamp relay control circuits in order to energize the battery saver relay and the interior lamp relay. When the relays are energized, voltage is supplied to the interior lamp circuits.