Gas gage defect

Yes. My 1951 Chevrolet has had that problem whenever the line gets corroded or is broken. General Motors gas gauges read full by default whenever there's an open circuit to the tank sending unit (variable resistor). The design sounds strange, but it is actually kind of a genius design. It is somewhat self balancing, and goes back to the days of mechanical voltage regulators and 3rd brush generators, where the electrical system might not be maintained at a perfect 7.4 volts all the time (14 volts in modern cars). The very newest GM cars might have a computerized affair, but well into the 90s the old system has been used. If you get an older Ford, which doesn't have the GM gas gauge system, the dash gauges must have their own voltage regulator. This helps keep them accurate.

T.