hey, i would appreciate all the help you lot can give me

i have a 96 turbo 2000 and the fuel gauge does not work, i have checked all that i can and have found that when the sender switch in the tank is connected to earth then the gauge works and moves to just over half tank of fuel, however when the floater is moved to empty the gauge does not follow. is this because i tested it out of the tank??? what could be causing this as i have used another sender switch and same problem. i understand that the needle will stay the same even if the car is turned off however when the floater that is meant to be in the tank is moved it only increases but fails to decrease towards empty.

all help very much appreciated cheers ppl

mo