OK, in the round harness connector the dark blue at top center is to fuel sender. A short distance counterclockwise is a blue with white tracer (about 10 o'clock position). This is 12 volts into the fuel gauge at switch on. This 12 volt supply along with the chassis ground at back of this gauge detailer earlier is all about the internal voltage limiter. The pulse voltage coming from that limiter jumps directly to the fuel gauge inside that gauge. This pulse voltage also comes out of the gauge at another of the posts so the printed circuit board can carry the pulse voltage to the water temp' gauge and the oil pressure gauge. The copper traces on these printed circuit boards are very simple to follow so you should be able to see and understand what I've described here.