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As I was driving my car the temperature gauge started to flucuate rapidly, then went to the 100. When you turn the key on ,you can see the needle move a little, but doesn't go past 100. How do you check the gauge to see if it is working or if it is the sending unit.
Disconnect the sensor wire from the sensor and ground it, if it pegs the gauge the wire and gauge are good. It sounds like your wire is loose on the sensor