Fuel gauge

We just bought an ex-MOD 1983 petrol 109, and it needs a bit of work -its been sitting in a field for the last five years. We changed all the ignition bits, and now it runs, but the fuel gauge always shows empty. It has two fuel tanks, with a changeover valve under the driver's seat. This is also wired to the two senders so that it switches the correct sender over to the single gauge, but it's not obvious (to me) how it should work. Both tanks have fuel in them, and it runs on either tank, so I have to assume the valve is working. Does anybody know anything about this setup, I've searched the net but found no clues?

I don't know about the military wiring but I'd guess it has a lot in common with the wiring on the civilian models. I'd check that the voltage stabalizer is working first of all. As far as I understand it the regulator (small rectangular box behind the dashboard) automatically switches the power to the guages on and off every few seconds to maintain an average voltage of about 10 volts. so turn on the ignition and check it does that first. You haven't mentioned that a problem with the temperature guage so it's probably not the regulator as both guages use it. If that's O.K. use the multimeter to check that the switch on the crossover valve is working properly. If that's O.K. Pull out one of the fuel level sensors, connect a multimeter to it to measure resistance at different angles. If that's O.K. then the problem might be the actual guage itself or faulty wiring. Good luck with it.

Hi, thanks for the advice. Turns out that both of the switches and one of the tank senders is open circuit, so I shorted one of the switches and wired the good sender to the gauge (which is OK). Replacement parts are on order.