Check the wire to the temperature sender, near the thermostat on the intake manifold. It might be a loose connection or a break in the wire. If not, touch one lead of an ohmeter to the terminal of the sender and the other to the manifold. It should read a few hundred or maybe a thousand ohms depending on the temperature. The sender is bad if it reads either a few ohms or millions of ohms.

 

Or you can just ground the wire going to the sender and if the gauge pegs it's working and it's probably the sender. If nothing happens the wire is broken somewhere between the sender and the gauge or the gauge is bad. The instruments in the dash pod share a common ground and if that was the problem other gauges wouldn't be working.

 

A common problem is a loose connector on the sender itself. Use a small punch to reset the rivet that holds it to tighten it up. Also the connector to the sender is usually another connection issue. You might have to put another connector on the wire. All the other advice is good.

 

I just replaced my gauge and sender. There are there are three wires on the back of the gauge. The one that attaches to the case is the ground the other two are power and sender. They should all be marked on the gauge back. Gigem75 has the quick test to see if it is the gauge or the sender.

 

Thank you all for your responses. Can someone please tell me how to remove the guage from the dashboard.

Mark

 

On the back of the gauge there are two posts. These hold a bracket that spans the gauge opening and pushes off the back side of the dash. The bracket is secured with with hex nuts or knurled nuts and a an external tooth lock washer.
If you can undo these two nuts the gauge will pop out the front with the wiring still on. I was able to access mine (1750) from the passenger foot well. Its tricky but possible.

 

Thanks for posting, this is something I need to tackle as well. Another item added to the laundry list of things to do