If it's the smiths sensor supplied by CAI 80C is approx 103 ohms sender resistance.You can measure the sender resistance to earth and check (disconnect cable first of course). You can then cycle the indicator using a 10Kohm pot' just one wire of the pot to engine block (earth) and the other connected to the signal wire from the sender to the gauge, ignition on and check the reading. These things are'nt manufactured to Natonal Physics Lab standards so the accuracy is not fabulous by any stretch. You may have the ford sensor though, which I think is a different set up.
