Water Temperature Indicator Gauge
WARNING: This page is about a different car, the 2004 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
The water temperature indicator gage is an ohmmeter that reads the resistance of the water temperature indicator sending unit. When the engine temperature is low, the resistance of the water temperature indicator sender unit is high, restricting the flow of current through the gauge and moving the pointer only a short distance. As the temperature of the coolant increases, the resistance decreases, allowing more current to flow through the gauge and resulting in a corresponding movement of the pointer.