Faulty TR6 Fuel Gauge? - Fix Lucas Electrics with a Voltmeter!

The Triumph TR, the MGB, even the XKE and Astons of the time... all used Lucas electrics. Lucas has a pretty poor reputation, but it's undeserved. In actuality, they were pretty robust. If you're having trouble with that overdrive switch in your Austin Healey, remember that the switch is probably 60 years old--well past the intended design life. A common issue with the Triumph TR6 (the Spitfire and GT6 too) is with the temperature and fuel gauges. These indicators are more or less both voltmeters that read the voltage of a circuit that includes a variable resistor of some kind (kind of like a dimmer switch). The fuel tank sending unit is basically just that, and the temp sending unit is similar but varies with heat rather than using a float like in the fuel tank. These gauges are supposed to operate on a fairly clean 10 volts, which is where a lot of problems with inaccurate readings happen. Rather than throw parts at the problem (why replace the fuel sender when that's not actually broken?), it makes sense to learn to check a couple things with a voltmeter. That way you can diagnose your trouble before spending any money. Replacing parts is not only more expensive, but it muddies the water in trying to find the original problem--because now you've made numerous changes trying to fix something... and may have thrown more things off. Hopefully this helps! Let us know what trouble you may have discovered!