Oil Pressure & Coolant Temperature Gauges

Coolant temperature and oil pressure senders are located on engine and send current to gauges through 2 magnetic coils and a sender. The sender controls gauge pointer operation by monitoring current flowing through the coils. The oil pressure sender is connected to junction of the 2 coils. It has low resistance when oil pressure is low and 90 ohms resistance when oil pressure is high.

The coolant temperature gauge has one coil grounded directly, and the other is grounded through coolant temperature sender. The sender has 55 ohms resistance when coolant is at 260°F (127°C). Its resistance becomes greater at lower temperatures, approximately 1400 ohms at 100°F (38°C). This causes current through sender (and a coil) to increase as coolant temperature increases, thus moving the pointer.