With Gages

CIRCUIT OPERATION

Only those indicators and gages that are not described in connection with other circuits are explained in this circuit operation. See the circuit referred to for its complete operation.

TACHOMETER
The Tachometer displays Engine speed in rpm. Voltage pulses are taken from the ignition system and sent to the Tachometer. It responds to the frequency of the voltage pulses which increase with Engine speed. Solid state circuits process these pulses into a signal that drives the pointer of the meter.

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 Level Sender.

When the tank is low, the resistance of the Fuel Level Sender is low. A large flow of current passes through the E coil and the Fuel Level Sender resistor. This pulls the pointer towards E on the scale. When the tank is full, the Fuel Level 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 Fuel Gage is not affected by changes in the voltage of the system.

COOLANT TEMPERATURE GAGE
The Coolant Temperature Gage is also operated by two coils. Battery voltage is applied to both coils. One is grounded directly and the other is grounded through the Coolant Temperature Sender. The Coolant Temperature Sensor has 55 ohms resistance at 260°F (125°C) and its resistance increases at lower temperatures. Resistance is approximately 1365 ohms at 1OO°F. This causes the current through the Coolant Temperature Sender and one coil to increase as the coolant temperature increases and moves the pointer.

OIL PRESSURE GAGE
Engine oil pressure is indicated by the Two Position 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 is connected to the junction of the two coils. It opens above 4 psi, sending current through the In-line Resistor to ground. This moves the pointer to the middle of the range, indicating normal oil pressure. A 68 ohm in-line Resistor keeps the indicator from going full scale with normal oil pressure.

VOLT GAGE
The Volt Gage measures the electrical system's voltage with ignition Switch in "RUN." With the Engine stopped, the Volt Gage indicates Battery condition. With the Engine running, the Volt Gage indicates Charging System operation.

SPEEDOMETER AND ODOMETER
The Vehicle Speed Sensor (VSS) generates a signal that indicates the speed of the solid state ECM to supply inputs to the Cruise Control Module, Speedometer and Odometer.

The Vehicle Speed Sensor is mounted in the Transaxle. A magnet rotates near a coil, producing voltage pulses in the coil. The frequency of the AC voltage coming from this coil depends on the vehicle speed. The VSS sends pulses to the ECM at the rate of 40,000 pulses per mile.

The ECM takes the voltage pulses from the sensor and uses them to close a solid state output switch. The output terminal is switched to ground at a rate that is proportional to the speed of the vehicle. The Speedometer and Odometer are switched at 4,000 pulses per mile.

"CHECK GAUGES" INDICATOR
The "CHECK GAUGES" indicator is controlled by a Solid State buffer located in the instrument Cluster. This buffer receives inputs from the Fuel Pump/Oil Pressure Sender/Switch, Coolant Temperature Sender, and the Generator. When any of these components indicate that a gage is out of the normal operating range, the indicator control circuit grounds the "CHECK GAUGES" indicator, causing it to light.

"LOW COOLANT" INDICATOR
The "LOW COOLANT" indicator receives battery voltage with the Ignition Switch in "RUN," "BULB TEST" or "START." The indicator is grounded by the Coolant Level Switch with the coolant level in the Coolant Reservoir below a minimum recommended level.

LOW FUEL INDICATOR
The Low Fuel indicator located in the instrument Cluster is controlled by a Solid State buffer which reads the same fuel level input sent to the Fuel Gage. When the resistance of the Fuel Level Sender drops below a certain point, the indicator control circuit lights the Low Fuel indicator.