Beltfed asks a key question at the top of this post. The value of R(t) - the total resistance of the circuit, including the guage windings and the sending unit, must be known if a voltage reducing resistor is being used. Since the sending unit's resistance is constantly changing, there is no one dropping resistor value that will maintain a constant 6 volts at the guage since R(t) is in a constant state of flux.
A mini- DC/DC convertor or, possibly a zener diode, is the only thing that I can see that would do that. My belief is that the "voltage reducers" available from our suppliers are simple resistors that give a "good enough" result even though the voltage is fluctuating at the guage. If someone has one of these on their rig, read the voltage at the guage when it's full, and then again when empty and let us know. My thought is that it won't be 6 volts in both cases.
