Easy way to tell, when the engine is up to running temperature..... shut the engine off, disconnect one of them, then turn the key back to "on" (don't start it though) and see if the gauge still registers the same. If you disconnect the gauge sender it should either go to full hot or not move, depending on if it's grounded against something as it's laying there.
My oil line fix
My 100k stopped odometer fix
Brace for impact, I'm in a "modifying mood". Massive thread count inbound.