Water temp gauge doesn’t work. Where to look first?

Pretty much as stated in the title. My water temp gauge doesn’t work. Where should I be looking to diagnose the issue? The gauge itself? The wiring? Thermometer?

What tests can I do to check where the failure occurs?

Remove the red/white wire from the water temp sender and ground it to the engine block.
Get in the truck and turn the ignition to ON... not start.
You should see the gauge slowly rise to the top of the scale.
Turn the key back off so you don't burn out the gauge.

If it does, the sender is bad and is simple to replace.
If the needle still doesn't budge you're going to have to remove the instrument panel so you can check the wire for continuity.