The Instrument Panel (I/P) Cluster Assembly receives power from either one or two IP Fuse Block sources. If Automatic Transmission, power runs from the TRANS fuse 20, through CKT 1020 (PNK) to pin 7 of the IP Cluster connector. If Manual Transmission, power runs from the GAUGES fuse 4, through CKT 39 (PNK) to pin 7 of the I/P Cluster connector. In both cases, the GAUGES fuse 4 supplies power to pin 22 of the I/P Cluster connector.

Power coming in through pin 7 of the I/P Cluster supplies voltage to the Tachometer, Electric Speedometer, PRNDL Indicator, and the Check Gauges Lamp Driver. Pin 22 of the I/P Cluster carries power to the remaining components within the I/P Cluster Assembly:

Ground for the I/P Cluster Assembly goes through two pins. One is pin 4, the other is pin 31. Both run to splice S215 and onto ground G104 and G103 (Gas Only).

Magnetic fields of two coils moves the pointer of the fuel gauge. The coils are at right angles to each other. Battery voltage is applied to the E-coil (empty) and the circuit divides at the opposite end of the coil. One path continues to ground through the F-coil (full). Another path goes through CKT 30 (PPL) to ground on single tanks using the variable resistance of the level sensor in the fuel pump and sender (Gasoline) or the fuel gauge sender (Diesel). On dual tank vehicles, CKT 30 (PPL) passes resistance from either the Vehicle Control Module (VCM) (Gas) or the Fuel Pump Balance Module (Diesel).

On gasoline vehicles with dual tanks, the VCM sends a 5 volt reference through CKT 474 (GRY) to the Fuel Pump Balance Module. The Fuel Pump Balance Module sends out a fuel level signal to the senders through either CKT 970 (DK BLU/WHT) for the Primary Sender and CKT 975 (LT BLU) for the Secondary Sender. Ground for both senders runs through CKT 900 (BLK) to the VCM. The Fuel Pump Balance Module will send the return voltage to the VCM through CKT 1589 (PPL/WHT) and the VCM will send the signal onto the Fuel Gauge through CKT 30 (PPL). The fuel pump balance module averages the resistance for vehicles with two fuel tanks. When the tank is low, the resistance of the level sensor is low. A large current flow passes through the E-coil and the pointer moves toward E on the fuel gauge. When the tank is full, the level sensor resistance is high, and less current passes through the E-coil, and the pointer moves toward F on the scale. With two coils operating the pointer, the fuel gauge is not affected by changes in the system's battery voltage.

On diesel vehicles with dual tanks, CKT 30 (PPL) runs directly to the Fuel Pump Balance Module. Grounds for the two fuel tank senders run directly to G104. The remainder of the operation is the same as gasoline.

For single fuel tank vehicles, the fuel gauge includes the following functions:

For dual fuel tank vehicles, the fuel pump balance module does the following functions:

When the level in the front tank increases to about two gallons greater than the rear tank, the secondary fuel pump stops. This then empties the rear tank first.

The oil pressure gauge displays the engine oil pressure. Current flow through two coils moves the pointer of the gauge and is similar in operation to the fuel gauge. The oil pressure sender senses engine oil pressure sending resistance through CKT 31 (TAN) to pin 15 of the I/P Cluster.

The oil sender has a low resistance (approximately 0 ohms) when the oil pressure is low (0 psi), and a high resistance (approximately 90 ohms) when the oil pressure is high (80 psi).

The temperature gauge displays the engine coolant temperature. Current flow through two coils moves the pointer of the gauge and is similar in operation to the fuel gauge. The engine coolant temperature sender sends resistance through CKT 35 (DK GRN) to pin 13 of the I/P Cluster.

The engine coolant temperature sender has low resistance at higher temperatures. The sender has a resistance of approximately 49.5 ohms at 123°C (260°F). The sender resistance increases at lower temperatures and is approximately 1305 ohms at 47°C (100°F). This causes the current through the sensor to increase as the coolant temperature increases and the temperature gauge pointer then moves toward the hot end of the gauge.

The voltmeter measures the electrical system's voltage when the ignition switch is in the RUN or START position. The voltmeter measures battery voltage when supplied to the instrument cluster.

With the engine running, the normal reading is between 12-16 volts. The indication may decrease to 9.5 volts in cold weather with the engine stopped and ignition in the RUN position.

The Low Coolant Level Indicator only illuminates to warn the operator when the surge tank has a low coolant level. Battery voltage is applied to the Low Coolant Level Indicator Module from pin 25 of the I/P Cluster through CKT 68 (YEL/BLK) when the ignition switch is in the RUN or START positions. The Low Coolant Level Indicator Module monitors the resistance of the Low Coolant Level Sensor. The level sensor has a high resistance of 50,000 ohms or more when the coolant level is low. This is the set point at which the Low Coolant Level Indicator Module grounds CKT 68 (YEL/BLK) in order to illuminate the low coolant lamp.

The Speedometer, grounded through the I/P Cluster ground circuit, receives its speed signal from either the VCM (Gas) or PCM (Diesel) through CKT 389 (DK GRN), which connects to the I/P Cluster at pin 14.

The tachometer, also utilizing the I/P Clusters ground, displays the engine speed in revolutions per minute (RPM). Voltage pulses are taken from the ignition control (Gasoline) or the generator (Diesel) through CKT 121 (WHT) and sent to the tachometer through pin 6 of the I/P Cluster. Solid state circuits convert the pulse frequency in order to move the pointer of the tachometer.

The PRNDL indicator shows the gear selection for an automatic transmission (AT). Voltage for the PRNDL indicator comes through pin 7 of the I/P Cluster. The following four circuits pass coded input from Transmission Range (TR) Switch (part of the park/neutral position (PNP) switch) to the solid state within the PRNDL indicator.

The illuminated gear selection depends on the combination of circuits grounded. Refer to PRNDL Logic Input Test for indicator combinations.

The check gauges lamp illuminates when the engine oil pressure is low or the engine coolant temperature is high.

The instrument cluster's check gauges lamp driver, solid state logic, monitors the input signals to the oil pressure gauge and the temperature gauge.

When the ignition switch is turned to the RUN or the START position, the check gauges lamp driver grounds the check gauges lamp when either of the input signals exceed the set point. this causes the lamp to illuminate. The lamp is normally illuminated when the ignition switch is turned to the RUN position. The lamp turns off when the engine is started and the oil pressure increases above the set point. All connections of the check gauges lamp driver are within the I/P Cluster Assembly.

Power for the Water In Fuel Lamp is supplied by pin 22 of the I/P Cluster. Ground for this lamp is provided by the Water In Fuel Sensor, located on the Fuel Filter housing. When water is detected by the sensor, solid state internals within the sensor provides ground through CKT 508 (YEL/BLK) and pin 18 of the I/P Cluster Assembly.