Erratic Temp gauge.

[SMatson802@aol.com]

I have a '71 spitfire which just started some bizare temp readings.  Start 
up, reads cold and gradually comes up in temp reading.  It then just keeps 
going til it pegs.  The engines is cool enough that I can put my hand on the 
thermostat housing.  The radiator is warm, so coolant is circulating.  What 
can be causing the temp to read so high.  
I checked the lead wire from the temp sending unit and it does not seem to be 
shorted out on the engine end of things.
Thanks in advance.
Steve in Mass.