my 78 guage never worked, found out that the PO had disconnected the wires. after i hooked them back up, it still didn't work and i checked with an ohm meter and a test light and eliminated that it was not getting any current. i had to drop my tank because the jeep would die when you put it in gear and under a load (it would run forever at any idle sitting there in neutral), and cleaned it and sealed it with POR to eliminate the problem the gas tank was full of crud (mud and rust), i replaced the float (it was half full of gas) and the pick up filter. while i had the sending unit out, i took it apart (probably not reccommended) and put it back together, and rigged it over a five gallon bucket, using the fuel guage and a test light and finally got it to working by using rust remover and a knife and cleaned it up. i was able to move the gauge to full if i clipped directly to the backside of the unit and bypassed the needle that moves along the winding when the float moved, but could not get the gauge to budge when it was wired up correctly until i cleaned off the back part of the unit where the needle made contact. if you look at the john strenk pages and pictures you can see what i am talking about. everything was rusted and corroded before i cleaned it up. once i did that, i made sure the guage worked with the unit in the bucket and then put it all back toether. it has worked fine since. your problem sounds similar. during the cleaning process, i did not have that plate completely cleaned, and on several attempts, the gauge would only go to half full, even though i would physically move the float, of course when you take the float all the way up and the lever arm touches the unit frame, it would jump to full. i started messing around with mine because i;m a cheakskate and also figured that something with so few moving parts, sitting in a tank of gasoline, shouldn't go bad. i just hadn't counted on the rust. getting the tank out was a pain in the ***, but easy. dirty, but easy. probably worth a look. of course, once you have it out, you could go to a parts store and replace the unit. as long as you have it out, if you have it out, i'd replace the filter as well.