Is it the ECT or somethign else? Is it a stand alone temp sensor or mechanical deal? If so, does anyone know where it's located? I'm just curious as to how accurate it is and where it's reading from.
The sensor referenced in the pic is the factory electrical sending unit for the factory temp gauge. If you choose to add an aftermarket electrical temp gauge it will come with it's own sending unit that can be installed in several locations, one of which is where the factory one is. Some guys buy a different t-stat housing which has threads for another sending unit, this way you can run both if you want.
That's what I just did - there is a place on the top center of the housing that is custom made for it. Use a 9/16" drill (neched down to 1/2" for a drill) and a 3/8" NPT tap to do the job.