Instrument Panel, Gauges and Warning Indicators: Description and Operation

Gauge failures are often caused by defective wiring or grounds. The first step in locating trouble should be a thorough inspection of all wiring, terminals and printed circuits. If wiring is secured by clamps, check to see whether the insulation has been severed thereby grounding the wire. In the case of a fuel gauge installation, rust may cause failure by corrosion at the ground connection of the tank unit.

VOLTAGE LIMITER TYPE
The voltage limiter type indicator is a bi-metal resistance type system consisting of a voltage limiter, an indicator gauge, and a variable resistance sending unit. Current to the system is applied to the gauge terminals by the voltage limiter, which maintains an average-pulsating value of 5 volts.
The indicator gauge consists of a pointer which is attached to a wire-wound bi-metal strip. Current passing through the coil heats the bi-metal strip, causing the pointer to move. As more current passes through the coil, heat increases, moving the pointer farther.
The circuit is completed through a sending unit which contains a variable resistor. When resistance is high, less current is allowed to pass through the gauge, and the pointer moves very little. As resistance decreases due to changing conditions in system being monitored, more current passes through gauge coil, causing pointer to move farther.

VOLTAGE LIMITER TEST
1. Connect one lead of a suitable voltmeter to temperature sending unit and other lead to a good ground. Do not disconnect sending unit lead from sending unit.
2. Turn ignition switch to the "On" position and observe voltmeter.
3. A fluctuating voltmeter indicates that voltage limiter is operating.