Automotive electrics has always seemed a black art to me - this problem has me stumped. My 403 gauge was working ok up to a couple of months ago, but then it started reading full all the time. I have checked all the wiring, tried swapping over gauges and even bought a new fuel sender unit from Franzose, but the problem persists. Can someone explain to me what the gauge actually measures - is it variations in current, resistance, or something else? And before you ask - yes, the tank is only half full.