I did receive a request for a copy of the data on temp and fuel gauge sender resistances, so here it is. I borrowed a "power decade box" from my employer at the time, and substituted it for each of the senders. I fiddled around with the resistance values until the gauges stabilized at each of the indicated readings. The data was taken on my '67 1A Tiger, which was assembled in September of 1966 (according to Norman).
Fuel Gauge Gallons Ohms 2 145 4 80 6 55 8 38 11 21 Temp Gauge Degrees C Ohms 60 150 80 77 90 57 100 41 120 24
The thermostat mentioned yesterday opened at 180 F (82 C). So, if you were to connect your ohmmeter to the sender, it should read in the mid to low 70's when the thermostat opens. Remember, this is automotive stuff, as well as being Lucas related, so don't panic if you can't reproduce these numbers exactly. Close is fine.
Another point: While the gauges may have adjustments, we don't know what to do with them. At exactly what input level do you make each of the adjustments? The factory probably had a procedure involving simulating different input levels and tweeking the adjustments to give the right readings, to wind up with reasonable accuracy over the whole scale. If you don't know the procedure, you may end up with the "fat lady and the girdle" scenario. Squeeze it in here, but it pops further out over there. I seem to recall having great plans to tweek the accuracy of my Smiths voltmeter (a thermal device not unlike our temp and fuel gauges), and then going crazy for a while trying to get it back to the accuracy I started with.