Speedometer

For operation of the instruments and of the warning lamps related to the exterior lamps, a common earth is provided from the instrument pack (C233-1) on a black wire.

For operation of the odometer illumination and of the instrument pack background illumination, an earth is connected between the instrument pack (C233-8) and the earth header joint (C017-5 for LH drive; C018-3 for RH drive), via the header joint and the passenger compartment fuse box. On vehicles without an illumination dimmer, a black wire is used. On vehicles with an illumination dimmer, a black/yellow wire is used between the instrument pack and the illumination dimmer (C201-1), then black wire is used from the illumination dimmer (C201-2) to earth.

Speedometer

The speedometer and integrated odometer are controlled by a road speed signal input to the instrument pack (C230-4), from either the gearbox mounted speed sensor (C195-3) on a white/orange wire (non ABS models) or the ABS ECU (ABS models, see ABS circuit for details), also on a white/orange wire.

Engine coolant temperature gauge

The Engine Coolant Temperature (ECT) gauge is controlled by a signal from the temperature gauge sensor. A green/blue wire connects the instrument pack (C233-2) to the temperature gauge sensor (C165-1), which is earthed through the sensor housing. The electrical resistance across the temperature gauge sensor is proportional to temperature, so the voltage of the control signal and the resultant deflection of the gauge pointer are directly related to coolant temperature.