Instrument Cluster / Carrier: Description and Operation

Circuit Operation

Engine Coolant Temperature Gauge
The engine coolant temperature gauge consists of two intersecting coils wound around a permanent magnet rotor. When voltage from fuse C-10 is applied to the coils, a magnetic field is generated. This causes the rotor to rotate and the gauge needle to move. The magnetic field is controlled by the thermo unit. As the resistance in the thermo unit vanes, current through the gauge coils changes. The gauge needle moves according to the changing magnetic field.

Tachometer
The tachometer displays engine speed in RPM. Voltage pulses are taken from the ignition system and sent to the tachometer. The tachometer responds to the frequency of the voltage pulses, which increases with engine speed. Solid-state circuits process these pulses into a signal that causes the gauge needle to move.

Oil Pressure Gauge (S Model)
The oil pressure gauge consists of two intersecting coils wound around a permanent magnet rotor (see engine coolant temperature gauge for operation).

Voltmeter (S Model)
The voltmeter measures the voltage through fuse C-10 when the starter switch is in ON or START

Indicators
The indicator lights are controlled by different conditions in their associated systems. See the associated system for the indicator light circuit description.

Bulb Check
With the starter switch in ON or START, battery voltage is applied to the "BRAKE" warning and charge warning lights. The generator will provide ground to the circuit until the engine is running. The lights go on to test the light bulbs and then go off after the engine is started.