I have the standard Chevy instrument panel and the temp guage just went crazy. I had the engine running in the yard and when I went back to it the temp guage was all the way up. I shut off the motor which was not overheating and now when the ignition is off the guage reads halfway and when the ign. is on the guage reads full up? Any ideas? Thanks Lloyd

Lloyd, I'm gonna guess that you have a Chevy engine to to with that Chevy instrument panel. On a big block, the temp sender is usually on one of the cylinder heads.

This is a starting point:

Check the connection for cleanliness and tightness. Check the wire for shorting out to ground. Turn on the ignition and remove the wire. Note the gage. Touch the connector to ground. Note the gage. What are they? The gage should be full hot one way, full cold the other way. Forgot which is which, but it is a good test of the wiring and gage with the sender eliminated.