Stupid Car! HELP!

I was actually experiences problems with my coolant temp gauge a couple weeks ago. It was jumping up and down like crazy when I would push the gas. After I cleaned the connector on the sensor, the gauge stopped acting up and read fine. I didn’t think that it was a problem. I beleive there are two coolant sensors. Am I correct? One for the Temp. gauge on the cluster, and another for the ECU. So which sensor would I replace, and how do I go about replacing it? Where can I buy a new one?