Use a multi-meter
The sending unit is a variable resistor. I think the range is something like 28 ohms - 150 ohms. To really check out this system, you'll wind up pulling the sending unit out to exercise the float arm. So, you might as well spend a few bucks, buy a new one and replace it. The thing is notoriously unreliable, widely available, and almost always the cause of these problems. West Marine stocks them on the shelf. To check this out with a multimeter, do the following... 1. Turn on the key, and measure voltage at the sending unit. One of the two terminals should have 12vdc. If not, the problem is power and not the sending unit. Trace the wiring back to the 12 volt source. 2. Assuming test 1 passes, remove and disconnect the sending unit. Connect an ohmmeter across the contacts, on a low setting. 3. Exercise the float arm while observing the resistance. It should vary about 100 ohms across the range. 4. If things are good so far, the only other possibility for this problem is a short on the plus side of the meter, but that is highly unlikely. If this is the problem, you would see the fuel guage pegged hard, and it would probably be smoked by now. good luck, Paul
