Goofy temp gauge

[atarijake]

If it's an electric gauge (not mechanical), you could take the gauge out of the dash and hook it up manually with a positive, a negative and a lead to the sending unit to the gauge. That way, you're sure the wiring is good. If the gauge still acts funny, it's either the sending unit or the gauge. I'd replace the sending unit first, cause it's cheaper, then the gauge.

I was able to diagnose my temp and oil gauge this way because I wasn't sure if the wiring was bad.

I was able to get a temp gauge for my 85 off ebay for about 20 bucks.