7.5 volts sounds right - these gauges are a bridge type electrically. The sender can be put in facing one of three ways, however. If it is in the correct position it should be pretty accurate. If it's in one of the other positions it either jams on the slosh baffle (never reads more than 1/3 of a tank) or the last quarter tank is only good for about 15 km if it's in the other wrong position. The trouble is, I can't remember which way around is which...