Don't apply power to the thermocouple leads (the yellow jacketed ones). Apply your 12v to the gauge with the thermocouple leads disconnected. The object is to turn the gauge "on" without having the input from the probe. All you're checking in this step is the gauge.

 

Thanks Cookie, I'll give it a try. Probably wont get to it till next week now though. Taking the kids deer hunting so going to be gone for a few days. I appreciate all the help from everyone.