Why doesn't the heater get hot and the temperature gauge is on hot? on 1998 Toyota Tacoma

I noticed that my heater was blowing cool air snd then the needle for the temperature went up to hot. When I turned off the heater the temperature went down some.

1 answer 2 comments
Does the engine actually get as hot as the gauge shows?
The engine did not overheat but the needle was on hot.
Sounds like a grounding issue; Check and clean all your grounds before going further, and coolant level.