sticking fuel gauge
 

This morning I filled up the Zed, completely brimmed the tank till the nozzle clicked, paid €55 for it all, gauge would only go up past half way, initially thought it was a fuel leak so when I got to the next garage I went to fill it again and it took less than €1 for the nozzle to click, gauge still stuck at half way and there is no sign of a fuel leak anywhwere around the filler neck/fuel tank etc.So I am fairly confident that it's either a faulty gauge or faulty sender unit, so. Where is the best place to start and how to test each unit? it was on just under quarter of a tank when filled
Thanks lads

Probably easier to check the gauge first and then the sender.

The sender is built into the pump inside the tank, to get to it you need to drop the tank.

Right, lets hope it isnt the sender unit so, I'm after driving the guts of 200 KMs and there's been no movement on the gauge, I'll take the instrument cluster apart tomorrow and check all the connections etc. Nobody here knows what kind of voltage/resistance readings I should be getting on the connections? I have a spare complete fuel pump in the shed so I might wire it all up and manually move the float to see if I'm getting any kind of change on a multimeter