Gages (U21)

The operation of an individual Indicator is described along with its circuit. Refer to the Schematic and text for the circuit that is indicated below each of the Indicators.

FUEL GAGE

The pointer of the Fuel Gage is moved by the magnetic fields of two coils. The coils are at right angles to each other. Battery voltage is applied to the E coil and the circuit divides at the opposite end of this coil. One path continues to ground through the F coil. Another goes to ground through the variable resistor of the Fuel Gage Sender.

When the fuel level is low, the resistance of the Sender is low. A large current passes through the E coil and the Fuel Gage Sender resistor. This pulls the pointer towards E on the scale. When the tank is full, the Sender resistance is high. More current now flows through the F coil, moving the pointer to F on the scale.

With two coils operating the pointer, the Gage is not affected by changes in the voltage of the system.

OIL PRESSURE GAGE

The engine oil pressure is displayed by the Oil pressure Gage. The pointer of the Gage is moved by two coils, and its operation is similar to that of the Fuel Gage.

The Fuel Pump/Oil Pressure Switch/Sender is connected to the junction of the two coils.It has low resistance when the oil pressure is low, and 90

ohms resistance when the oil pressure is high.This changing resistance changes the current flow though the coils. The magnetic fields of the coils move the pointer from low to high.

COOLANT TEMPERATURE GAGE

The Coolant Temperature Gage is operated by two coils. Battery voltage is applied to both coils. One is grounded directly and the other is grounded though the Coolant Temperature Sender.This has 55 ohms resistance at 127°C (260°F) and its resistance becomes greater at low temperatures. It is approximately 1365 at 38°C (100°F). This causes the current through the Sender and one coil to increase as the coolant temperature increases. This moves the pointer.

SPEEDOMETER AND ODOMETERS

The Speedometer is operated by an electronic circuit. The Vehicle Speed Sensor (VSS), located in the Transaxle, generates an AC voltage whose frequency is proportional to the speed of the vehicle. This goes to the Electronic Control Module (ECM) and then to the Speedometer circuit board in the Instrument Cluster. The Solid State unit drives the pointer of the Speedometer. There is no Speedometer cable in the vehicle.

The same buffered speed signal form the ECM is processed by the Speedometer circuit board to drive the odometers. They are operated by a Stepper motor that responds to pulses from the Speedometer circuit.

VOLTMETER

The voltmeter measures the electrical system's voltage with the Ignition Switch in RUN, BULB TEST, or START. With the engine stopped, the Voltmeter indicates Battery condition. With the engine running, the Voltmeter indicates Charging System operation.

TACHOMETER

The Tachometer displays engine speed in rpm.Voltage pulses are taken form the ignition system and sent to the Tachometer. Solid State circuits process these pulses into a signal that drives the pointer of the Tachometer. The Tachometer responds to the frequency of the voltage pulses. These pulses increase with engine speed.

LOW FUEL INDICATOR

The LOW FUEL Indicator located in the Auxiliary Gages Assembly is controlled by a Solid State buffer which reads the same Fuel Gage Sender input sent to the Fuel Gage. When the resistance of the Fuel Gage Sender Drops below a certain point, the indicator contr6l circuit lights the Low Fuel Indicator.

CHECK GAGES INDICATOR

The CHECK GAGES Indicator, located in the Instrument Cluster is controlled by a Solid State buffer located in the Auxiliary Gages Assembly. This buffer receives inputs form the Fuel Pump/Oil Pressure Switch/Sender and the Coolant Temperature Sender.When either of theses senders resistances indicate that a gage is out of the normal operating range, the indicator control circuit grounds the CHECK GAGES Indicator, causing it to light.

Additionally, the digital regulator in the Generator control the CHECK GAGES Indicator with a solid state lamp driver. The lamp driver turns on the indicator whenever an undervoltage, overvoltage, or a stopped Generator is detected.