Oil Pressure Gauge
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 instrument cluster sends a signal voltage to the normally open oil pressure switch. When low oil pressure is detected, the switch closes, grounding the circuit and causing the oil pressure gauge to display low pressure.