2003 Kia Sedona Temp Gauge replacement or adjustment?

Greetings;
I posted earlier that my temp gauge reads overheat but ECTS shows it really isn't.

Long story short, I did what all good amateurs do - I replaced the ECTS without going through all the diagnostics that could/should be done.
Yes - I am one of those "part swappers". At least I am not a professional mechanic that does it.

So - replacing the ECTS did absolutely nada, zip, zero for the problem.

How often do these gauges actually fail as compared to the wiring having an issue?

If in the circuitry, where does one begin to track this down? What other than a multimeter would I need?

Is it possible to "re-zero" a gauge like this?

Thanks in advance for all of your assistance.

poolside