[jimmmie '79 Cheyenne]

Had the same prob on mine a couple months ago. Got flustered trying to trace the wire and a buddy at work had an extra set of gauges. Swapped out the temp gauge and all was well. Did a little troubleshooting on the gauge and the resisitor on the back was bad. A place called "fix-a-gauge" has the part for about $8 or if someone else knows the size, you can get it at radio shack. Good Luck...