There are TWO temp sensors, one for the computer and one for the dash board gauge.
The 1 wire sender is for the gauge.
The 2 wire sensor is for the computer.
Remove the connector from the 1 wire sender, turn on key, temp gauge needle should go all the way up or all the way down, doesn't matter which way as long as it goes ALL the way.
Use a wire in the connector and ground it to engine, with key still on, the temp gauge needle should do the opposite of what it did above, ALL the way up or down.
If it doesn't go ALL the way in both directions then either the gauge or wire to the gauge has the problem.
If gauge needle does go all the way up and down then pull out sender and make sure threads at the bottom are clean, since this is a 1 wire sender it needs a good ground to the engine to work properly, so NO TAPE on the threads at the bottom.