You could try taking the sender out and manually moving it over it's range whilst looking at the gauge.....just to confirm. Might find it is stuck or will work over part of the range etc.
Might even get away with a clean up
So got it out wth your method. dont know why but I wasnt expecting it to look like the gubbins of a toilet!
Made the contact for the copper arm stronger by giving it a bit a of bend, pluged it in and played with it, fuel gauge copied my every move!!!!
Happy bunny and thanks for the hints. Coundnt get it back on the tank. was really tight, it seemed the seal would go on the pi55 every time i tried to screw it in. broke two of the lugs in the process!... in the end i made a T shaped tool, allen key across the two lugs with mole grips on the key.. peace of cake then.