[bestgenman]

A short primer on gauges, not all but most used.   The gauge is really a voltmeter so a +12, a negative, and a sense connect to the gauge.  The negative could even be eliminated but used to drive a digital display or a backlight on an analog gauge.     The sense is a resistor to ground I.e. oil pressure is a variable resistor modulated by pressure, a temperature sender uses a device that changes resistance as the temperature changes.  They can be direct or indirect.   That means the gauge could go full scale if the sender has 0 resistance as in direct or could drive the gauge to zero with zero resistance.

Example:  I had a new fuel tank built and the old sender didn’t work so I bought a new one the correct length , not paying any attention to the direct or indirect.  Installed the tank and walla, no fuel showing on the gauge.  At this point , I was sure I had forgot to remove the shipping pin and there isn’t enough room to extract the sender.  I decided to go back to the log book method, disappointedly giving up on the gauge.  Did a 600 mile trip and noticed the gauge was about half tank.  It then dawned on my thick old mind that the sender was not matched to the gauge as full on the gauge is an empty tank?. 

So, your temp sender is a resistor to ground, I would bet, and you could use the new sender replacing the old one. The sense wire   can be grounded driving the gauge to max low or high to determine if the wire is intact