Instrument Panel, Gauges and Warning Indicators: Description and Operation

INSTRUMENTS





DESCRIPTION

The fuel, temperature, oil and battery gauges are all air cored instmments. An air cored instrument can be considered as a magnet in a magnetic field. A bar magnet pivoted in its centre is mounted in the centre of three coils. To cause the magnet and therefore the pointer to move, the current flow in one of the three coils is changed, which in turn alters the magnetic strength in that coil.

The transmitter or sensors are all variable resistors, and are connected across or in parallel with one of the coils. As the resistance varies in the transmitter the current flow through the coil will also vary. This will alter the magnetic field strength causing the pointer to move.

ELECTRONIC SPEEDOMETER

The pulse signal required to operate both the speedometer (and where fitted, the service interval counter) is controlled by a speed transducer situated in the transmission unit in place of the angle drive. The service interval counter, NAS markets only, is situated in the boot compartment and is located by removing the rear detachable boot trim panel.

It is important to note that should the harness controlling the pulse input to the speedometer become disconnected at the speedometer, the service interval counter will also CEASE TO OPERATE. The control for resetting the speedometer is now situated in the speedometer fascia and is operated by depressing the control button.

TACHOMETER

The engine speed signal received by the tachometer is derived from the ignition coil negative terminal. The voltage wave-form at this point can reach as much as 400 volts when a spark is generated and it is desirable to suppress this voltage before allowing it into the wiring harness. If this is not done interference may occur with other signals. A resistor connected into the lead from the negative terminal of HT coil serves this purpose, and it is located inside the i9nition amplifier. The battery voltage required to operate the instmments is derived from fuse No.4.