The Oil Pressure sensor is placed on the oil circuit, it activates a warning light on the dashboard at specific critical pressure levels. This sensor will warn the operator of an oil circuit failure.
The oil pressure switch is normally closed. When the ignition is switched on, the oil pressure warning light illuminates. When oil pressure is built up as the engine starts, the switch contact in the oil pressure switch opens and the ground contact for the warning light is interrupted. The warning light goes out.