TR7 instrument cluster connections and cable colours

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Ignition - black/blue (fat)

Right indicator - purple/red

Left indicator   - black/blue (thin)

High beam       - Blue/orange

Oil                  - red/blue

Brakes             - blue/green

Choke              - red/orange

Low fuel           - Black/red

Rear fog           - black/green

Tacho sensor     - blue

Speedo sensor   - brown

Fuel sensor       - green

+ve always on   - yellow

+ve ignition       - red

Illumination       - white

Chassis/earth     - black

Instrument cluster cable colours

Above: gauge with coils at right angles, coils removed, magnet on needle shaft revealed.

Left: the magnet removed.

Right: the circuit diagram.

How gauges such as the fuel and temperature gauges work (in cars pre about the year 2000

Within the two coils wound at 90 degrees to each other is a magnet attached to the needle shaft of the instrument. An iron tube round the assembly reduces the influence of stray magnetic fields. This grease on the bearing surfaces of the needle shaft damp the movement of the needle. Adjusting the current through each of the two coils the magnet will line up with the resultant of the two magnetic fields. In the circuit above, this is achieved by the sensor altering its resistance. In the case of the fuel gauge, the sender consists of a float on an arm which slides a wiper over a wire-wound resistance as the float rises and falls, so altering the resistance.