Fuel gauge is wrong!

[Justin14100]

Know the feeling of only putting £5 in! haha

Think i'm going to remove the sensor from my old mk3 fox, that was v. accurate and went right down to the little stick!

[JimmyG40]

I've just bought my first 40 and the fuel gauge doesn't work. I've had a new tank put in it too, and checked the resistance from the ball cock sender unit when it was out and it was working, well it was giving me some resistance when i moved the arm up and down, put it all back in and back together and it still doesn't work. 

Apart from literally going along all the wiring through the car, has anyone got an ideas in how to find the problem, i was also gonna try another set of clocks to see if it was that too but haven't sourced any yet.

Any feedback will be appreciated.
Thanks!