Originally Posted by Richard Wooldridge

I think you are mistaken in the ground through the glow relay idea! According to my wiring diagram, the temperature sensor is screwed into the engine block, the ground for the engine is the heavy wire cable from the engine to the frame near the steering gear. The ground for the gauge (and most of the other instruments) is the main ground, located behind the instrument cluster. +12V is supplied through fuse 12 to the temperature sensor when the ignition switch is in the start or run position. Possible problems would be: 1. a broken wire from the temperature sensor to the instrument cluster - you can check that with an ohmmeter. 2. a broken or cracked trace on the instrument cluster board. (Most likely!) If you don't see anything, try resoldering all connections in the circuit path. This should be a fairly simple fix, I think.

Richard Wooldridge