Principles of Operation (How Does It Work)

The instrument cluster carries out a display proveout to verify that all warning/indicator lamps and monitored systems are functioning correctly. When the ignition switch is in the ON position with the engine off, the following indicators will illuminate:
^ CHECK ENGINE/Malfunction Indicator Lamp (MIL).
^ CHECK GAGE warning indicator.
^ Charge system warning indicator.
^ Anti-lock Brake Warning Indicator (ABS).
^ Safety belt warning indicator (60 second proveout).
^ Air bag indicator.

Printed Circuit
The instrument cluster printed circuit supplies current to the instrument cluster indicators and gauges. It is constructed of copper foil bonded to a polyester base film (usually referred to as Mylar (R)).

The instrument cluster printed circuit is mounted to the instrument cluster housing and, due to its location, cannot be easily tested or inspected in the vehicle. This makes the instrument cluster printed circuit vulnerable to damage when a probe is used for in-vehicle testing because the probe can pierce the instrument cluster printed circuit or, in some cases, burn the copper conductor.

Since there is no approved procedure for in-vehicle testing of the instrument cluster printed circuit, the instrument cluster must be removed from the vehicle for visual inspection. If no damage is evident, each circuit should be checked with an ohmmeter. If an open circuit or a short is detected, the instrument cluster printed circuit must be replaced.

Gauge Indication Systems
The indication Systems use magnetic gauges mounted in the instrument cluster. All the gauges are constructed with windings that form coils. Typically one coil is wound at a 90° angle to the other two. The coils form a magnetic field which varies in direction according to the resistance of the sender, except the battery voltage gauge, that is connected between two of them. The battery voltage gauge varies in direction according to the battery voltage. A primary magnet, to which a shaft and pointer are attached, rotates to align to this primary field, resulting in pointer position. No instrument voltage regulator is used with this system. No adjustment, calibration, or maintenance is required for any gauges.

Instrument Cluster Gauge Amplifier/Check Gauge Module

NOTE: The fuel gauge and instrument cluster gauge amplifier must be replaced as a set. The fuel gauge and instrument cluster gauge amplifier are calibrated together.

The instrument cluster gauge amplifier electrically averages the fuel sender readings so the gauge displays the actual fuel level and not the fluctuations due to fuel sloshing. The amplifier also supplies the signal to illuminate the CHECK GAGE indicator (if equipped) to indicate low fuel, high engine coolant temperature, or low engine oil pressure. The gauge amplifier is a small printed circuit board located in a pocket on the back of the instrument cluster. The electrical connections are made with a spring-type connector. There are no provisions for calibration or adjustment. The fuel gauge and the instrument cluster gauge amplifier must be replaced as a unit.

Fuel Sending Unit
The fuel sending unit is a variable resistor made up of a ceramic substrate. It is controlled by the action of a float arm. When the fuel level is low, resistance in the unit is low. When the fuel level is high, the resistance is high.

Water Temperature Indicator Sender Unit
When the engine temperature is low, the resistance of the water temperature indicator sender unit is high, thus restricting the flow of current through the gauge and moving the pointer only a short distance. As the temperature of the coolant increases, the resistance decreases, allowing more current to flow through the gauge and resulting in a corresponding movement of the pointer.

Oil Pressure Indicator Sender Unit
The oil pressure switch is installed in the engine block and consists of a diaphragm and contact points. The contact points are closed with oil pressure, causing the gauge to indicate NORMAL oil pressure. With no oil pressure, the contacts open and the gauge indicates low oil pressure.

Charge Indicator System
The battery voltage gauge measures the voltage potential at the battery.

Vehicle Speed Signal
On vehicles equipped with 4-wheel Anti-lock Brake Systems (4WABS), the vehicle speed signal is generated by the rear anti-lock brake sensor and sent to the 4WABS module. The 4WABS module sends the vehicle speed signal via circuit 679 (GY/BK) to all systems which require a vehicle speed signal input. Vehicles equipped with Rear Anti-lock Brakes (RABS) generate a vehicle speed signal from the rear axle speed sensor. The Generic Electronic Module (GEM) receives this signal (VSS_GEM) for internal use and then distributes it to the appropriate other users, (i.e., the PCM, speed control module, and speedometer).

Speedometer
The electronic speedometer receives a speed signal from the 4WABS module (if equipped with 4WABS) or the GEM/CTM (if equipped with RABS).

Odometer
A million-mile tamper-resistant odometer is standard. Replacement speedometers have a resetable odometer.

NOTE: Some state laws require that the odometer in any replacement speedometer must register the same as on the removed odometer. Replacement speedometers and odometer modules with the mileage preset are available through Ford electronic repair centers.

If the actual vehicle mileage cannot be determined, the repair centers are able to supply odometers set to "0" miles. An odometer mileage sticker is supplied with the replacement odometer. This sticker must display the estimated vehicle mileage and be affixed to the driver doorjamb.

Trip Odometer
The trip odometer indicates how many miles the vehicle has been driven since the last reset.

Tachometer
The tachometer is a 6000 rpm tachometer.It has four terminals labeled "B" (12 to 14.5 V), "S" (EDIS tach signal in), and two "6" (cylinder selection grounds). The top ground (G) terminal is open on a 4-cylinder engine vehicle, and is grounded on a 6-cylinder engine vehicle.

Warning Indicators

Brake System
All vehicles use a brake system warning indicator in the instrument panel to warn of system malfunctions. The red brake warning light (BRAKE) is used to indicate a low fluid level, a brake malfunction, or a parking brake that is not fully released. The brake fluid level switch is located in the brake fluid reservoir.

The yellow brake warning indicator is used to indicate a malfunction or deactivation of the Anti-lock Brake System (ABS). It illuminates when triggered by the ABS control module, and stays illuminated as long as the malfunction remains in the system.

Charge System Warning Indicator A red charge indicator is located in the instrument cluster. This indicator illuminates when there is low or no generator (GEN) output.

When the ignition switch contacts are closed, battery current flows through the charge indicator and the parallel resistor (390 ohms) to the voltage indicator, and the indicator comes on.

When the generator builds up enough voltage to energize a circuit in the voltage regulator, the indicator goes out.

Check Engine Light
The CHECK ENGINE/Malfunction Indicator Lamp (MIL) is illuminated when a Diagnostic Trouble Code (DTC) is sensed in the closed loop by the Powertrain Control Module (PCM).

Air Bag
If an air bag system DTC is detected, the air bag indicator is illuminated.

Safety Belt
The safety belt warning indicator is powered through the GEM/Central Timer Module (CTM). When the ignition key is turned on, the indicator illuminates for four to eight seconds, even if the safety belt is buckled.

Low Fuel
When the fuel level drops to a predetermined level, the CHECK GAGE indicator will illuminate (if equipped).

Door Ajar
The DOOR MAR indicator illuminates when any of the vehicle doors are open.

High Beam
This indicator is illuminated when the high beams are on.

Overdrive Off
The O/D OFF indicator will illuminate when the transmission is locked out of gear. This dual function indicator will also blink off and on if a transmission fault is detected.

Anti-Theft
The theft warning system provides the vehicle with protection from unauthorized entry into the passenger compartment and engine compartment (hood opening). If triggered, the system provides both audio and visual alarm signals and disables the starter circuit.

The system is controlled by the Remote Anti-theft Personality (RAP) module. When armed, unauthorized entry into the vehicle is detected by the door open warning lamp switches and a hood switch (located on the right front fender apron). In addition, the system triggers an alarm if the ignition lock cylinder is forcibly removed from the steering column.

Once triggered, the system flashes the low beam headlamps, the parking lamps, the THEFT indicator, and sounds the horns.

Speed Control
The Speed Control (SPEED CONT) indicator lamp will illuminate when the speed control is engaged.

Fuel Reset
The FUEL RESET indicator is grounded through the inertia switch whenever the vehicle is subjected to a high force situation. The Inertia Fuel Shutoff Switch (IFS switch) cuts off the fuel pump motor.

The fuel cutoff system is a safety feature in the event of an accident. The FUEL RESET indicator (if equipped) will illuminate, indicating that the inertia fuel shutoff switch must be reset before the vehicle can be operated.

Check Gage
The CHECK GAGE indicator (if equipped) will illuminate if any of the following occur:
^ Engine oil pressure drops below approximately 42 kpa (6 psi).
^ Fuel level drops below approximately 4-8 L (1-2 gal).
^ Engine temperature exceeds approximately 121°C (250°F).