The engine temperature gage is "looking" for a ground to indicate maximum temperature. If you turn the key on (don't start the tractor), take the wire off the temperature probe and put it to ground for a couple of seconds, you should see your temperature gage read maximum. Since both your gages are failing, I think you probably have an open rather than a short in the circuit. I'd ask Glen at McMaster's to replace the instrument cluster with a known good one and see if the problem goes away. If it doesn't, it's probably a loose power connection or an open instrument cluster connector. Do your "idiot" lights work in the instrument cluster? If they do, that means the cluster is receiving power.
Just a few thoughts.... Intermittent problems are the worst kind to troubleshoot. /forums/images/graemlins/tongue.gif