Fuel pump / sender issue

[jonnow]

Hi, I have a 2002 9N, 16v 1.4 petrol. For some time now the fuel gauge has been giving incorrect reading - eg only half full when actually full -and not showing empty when it is. I took it out of the tank today and checked it over - and whilst out of the tank I reconnected the wires and with the ignition turned on, I tested the operation of the float by moving it up and down- and the gauge responded correctly. I then put it back in to the tank and it went back to not working… I took it back out again, it worked - put it back in and it didn’t work… I just don’t know what to do next - is it the unit playing up when immersed - or is it the guage - or the wiring? Please help!