The fuel gauge in effect measures the resistance on the line to the sensor in the tank. When the tank is full there is very little resistance but as the fuel level lowers the resistance is increased. The fuel gauges are notoriously susceptible to a bad earth between the sensor in the tank and the negative pole of the battery. Naturally this normally passes through the chassis and it may be that you have a bad connection somewhere. I was told at Caerbont Automotive Instruments (Smiths) that they had a lot of problems with the London taxis and in the end recommended a direct earth line from the earth on the sensor to the battery.

Peter

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