Safety Belt Warning Indicator
WARNING: This page is about a different car, the 2004 Ford RV Cutaway, 2004 Ford Econoline, 2004 Ford E450 Super Duty, and 2004 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
The driver safety belt switch is hardwired to the instrument cluster. When the safety belt is engaged, the driver safety belt switch grounds the circuit, causing the lamp to turn off. When the safety belt is unbuckled, the ground is removed and the instrument cluster illuminates the safety belt warning indicator.