Probably the temp sending unit.
There are several things that can cause your 2001 Ford F2 50 outside temperature gauge to quit working. The most common cause is a malfunctioning outside temperature sensor.
If your temperature gauge isn't working the problem is a bad gauge, grounded or disconnected wiring or, most likely, the temp sender isn't working.
temperature gauge not working can be caused by a bad temp sensor in engine, a bad gauge in dash, or a bad fuse
Check to make sure that the temperature sensor is good. A bad sensor is commonly the cause of the temperature gauge not working.
An inoperative temperature gauge will not alter how an engine runs, but the operator will not know if the water temperature has risen above normal without a properly working guage.
It is possible that the temperature gauge has stopped working in a 1992 Tempo due to a blown fuse. It is also possible that the temperature gauge stopped working do to the temperature sensor in the engine having a short.
Most likely cause is a faulty coolant temperature sensor.
Most likely, the temperature gauge's connection is loose. It is usually on the thermostat. An inoperative temperature gauge will cause most check engine lights to come on.
The most likely cause is a broken wire or blown fuse.
Temperature gauge not moved and the fan's always are working
most likely the gauge
The relay sensor is likely defective