I have these controllers new for $50.  This problem could also be caused by a
break in the wire going to the sender.  Use a continuity tester and connect
it to both ends of the wire (you can unplug it in the engine compartment).
Now test for continuity.  Now wiggle the wire.  Any difference?  If the wire
has a bad spot this should find it.
Hope this helps.
Ken Wilford
Van-Again
John 3:16