The sending unit is either defective or it is hanging on something in th tank.
on the side of the radiator
Yes.
your float could be stuck
1990 Chevrolet Lumina temperature sender is located on the back side of the thermostat housing. The sender has a wire that goes to the temperature gauge.
It's a GM
The gauge is part of the fuel pump/float assembly within the gas tank. It is probably a $500.00 repair. It is harmless.
Check for power and ground at the tank. If it is okay then the sending unit is most likely the cause.
$600 for a new pump, sending unit and labor
Install a manual gauge to check actual pressure or try Replacing oil sending unit
A pretty reasonable assumption would be the thermostat is stuck open.
Yes, you splice a small length of 16 gauge wire to 18 gauge wire for a repair.
Check actual engine temperature with a thermometer--if in acceptable range temperature sensor or gauge may be defective