In searching some old posts I came upon one from Paul.....

In my 87, It was my impression that the sender in the termostat housing was the sender for the temp gauge. Pauls post suggests its for the aux fans. I've pulled the fans along with the condensor.
Any reason I can't just pull that sensor and replace with one for a generic gauge? Does it do any thing besides controling the fan?
I figure I have to remove the t-stat housing for my leak problem anyway...so why not take the opportunity to replace it with something I can use.

I'm afraid you're going to be hard pressed to find an aftermarket guage sensor that is small enought that it will fit in the exisiting mounting for the sender for the aux. fans. Long story short, been there, done that, wound up plumbing it into the heater supply hose.