Checking engine temp gauge

[earl84]

My truck has not been run all that much, but it has been run a little. I just finished doing the entire AAW wire harness install and have run the engine since then and the temperature gauge stayed in normal operating range. Prior to that, the PO had an aftermarket gauge on it and it ran in the normal heat range. I removed that (now I wish it was still installed) because I want to go back to close to original look.
Anyway, I got my heater core fixed at a locla radiator shop, reinstalled it, and connected everything up. This was sort of the last thing of MANY little projects to do prior to calling it roadworthy. Well, I went for a very short drive, and the factory temp gauge was quickly heading to the danger zone. I pulled over and let it cool, then brought it back home. Checked coolant level, good. Checked for any water in oil, good. Keep in mind, it has run before and there were NO issues. The engine was not overheated, didn't smell hot, nothing.

There were only two things different than prior when it was running normal temp. One was the heater core, so I bypassed that and the temp gauge was still showing it getting hot. The heater core was flowing water through it just fine when I shot a water hose through it.
The other was that I pulled the gauge cluster out to clean up some other wiring, and also had to mess with the wiring that ran to the back of the alternator and the temp sensor on the engine (they run together in some nylon braided sleeving. So maybe I pinched the green wire for the temp sensor to the temp gauge. Hope not.

So what is my question after that long diatribe? Is there an easy way to check whether my temp gauge is bad? Or my wiring? I guess I could check for continuity and/or run another temporary wire in the engine compartment and see what happens.

I am thinking of getting another cheap temp gauge and installing that, just for troubleshooting purposes. Is there a better/easier alternative?

Sorry for the long post, just thinking as I type and trying to give a complete picture of what I have done and am thinking.