I got to thinking some more about this problem. I took the gauge out of the dashboard and found that if I grounded a certain terminal on top of the gauge itself it reads properly. It seems that over the years, extra resistance has built up inside the gauge itself and results in a bad ground i.e. there is extra resistance in the circuit where the gauge should go directly to ground causing the gauge to read full. Anyway, I broke one of the tiny, tiny wires in the gauge causing it to not work at all as I was putting it back together so now it is out for a total rebuild. So FYI to anyone experiencing the same problem, disassemble the gauge, ground the upper rightmost terminal when viewing the gauge from teh front and see if that doesn't fix the problem. Just be very carefull when reassembling.
