Oil Pressure Indicator Sender Unit
WARNING: This page is about a different car, the 2002 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
The oil pressure switch is installed in the engine block and consists of a diaphragm and contact points. The contact points are closed with oil pressure, causing the gauge to indicate normal oil pressure. With no oil pressure, the contacts open and the gauge indicates low oil pressure.