Instrument operation

INSTRUMENT OPERATION

Instruments

Speedometer

The speedometer receives a 12 volt ignition supply from fuse 8 on the Y wire and an earth path is provided on the B wire.

Pulses from the speed transducer are integrated and converted into an analogue voltage which increases as the vehicle speed rises. The moving pointer of the speedometer displays vehicle speed against a scale calibrated in MPH and KPH.

Tachometer

The tachometer receives a 12 volt ignition supply from fuse 8 on the Y wire, an earth path is provided on the B wire and an input from the MEMS control unit (T-Series 2.0) or Bosch ECM (L-Series) on the W/B wire. The moving pointer displays engine speed against a scale calibrated in RPM.

Temperature Gauge

The temperature gauge receives an ignition supply from fuse 8 on a Y wire and is earthed by the B wire on the instrument pack. The gauge receives a signal from the engine coolant temperature sensor on the Y/G wire. When the coolant temperature is low, the resistance of the temperature sensor is high, reducing the current flowing through it and causing the gauge to indicate a cool temperature. When the coolant temperature is high, the resistance of the temperature sensor is low, increasing the current flowing through it and causing the gauge to indicate a hot temperature.

Fuel Gauge

The fuel gauge receives a 12 volt ignition supply from fuse 8 on the Y wire and an earth on the B wire.

Voltage is applied across the fuel tank sender unit creating a current in the Y/W wire. When the gauge unit float is at its lowest point, indicating an empty fuel tank, the resistance is high producing a low current in the Y/W wire causing a small deflection on the gauge.