needle on both gas and temp guages suddenly going out the top of the guage

[battlecat]

My 1980 GL 4wd wagon has not been driven alot lately (had some brake problems) but yesterday I fixed the brakes and cranked her up and took out for a test run. Suddenly both the gas and temp guages began to malfunction (the needle rose slowly out the top of both guages. No other guages (oil pressure, speedometer, tachometer) appeared to be malfunctioning. I shut her down, restarted, same thing happened. I then disconnected the negative battery terminal, left if off a few seconds, then reconnected. No change. Disconnected negative terminal again, left it off overnight (believing that maybe I was resetting the CPU???). This time the temp guage rose normally, but the gas guage needle rose out the top as before. The only thing I can think is that I inadvertently let the battery go completely dead a few weeks ago when I left the hatch ajar and the dome light ran down the battery. Does anyone know what might be the problem here?

[naru]

No CPU to reset.

 

Fuel gauge circuit has high resistance.Bad connections or corroded sender.

[battlecat]

Thanks, Naru! I'll check the connections. I wonder how it occurred that BOTH guages began to malfunction at the same time?

[Caboobaroo]

They probably have a shared ground under the dash. I remember there being one down by the hood release handle that can make the gauges act funny.

[battlecat]

They probably have a shared ground under the dash. I remember there being one down by the hood release handle that can make the gauges act funny.

AHA! That is entirely possible! I will check that out, thanks Caboobaroo!!