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It doesn't work on volts or amps. It is pulsewidth modulated to ground by the ECU. I'm sure you could probably activate it also by a variable voltage, but that isn't how it is operated now. One side of the gauge is +12 vdc, the other connects to the ECU, to a driver chip, which is controlled by the CPU.
Well, I don't have a MMC ECU so it doesn't do anything at the moment. I spotted that the Innovative LC-1/DX-16? has what I understand to be an adjustable/programmable secondary voltage out put. My plan was to hook it up to the dash gauge, but it sounds like it wont really turn out.
You just need a little rc circuit that will turn a voltage into a pulse-width. You could make one with a 555 timer chip and some resistors / capacitors. Otherwise I'm SURE that you could buy one pre-made. The issue will just be getting the voltage to PW curve to match up to the LC1 output and the gauge input.