1998 Ford Escort temp gauge

Just bought the car last week.
only problem is that the temperature gauge
is all the way over past the hot even when the car is off. It seems to go up a little when the car is running.
I unplugged the wire to the sending unit and the gauge goes down to normal. (Cold)
I went to replace it but when I got to disconnecting the connector, I found only 1 wire leading to it.
the connector has 2 prongs. Is it supposed to have 2 wires?
do I just replace the sending unit?
I guess I need to look at another car to see the correct way it is supposed to be hooked up?