fuel sender problem

Hi all i have just converted my A4 2.5tdi convertible FWD 2003 to a Quattro. All is well apart from the fuel gauge. I have used the existing plug for the drivers side sender unit and jumped 2 wires across to the sender on the passenger side. The cables arut e the same colours in mine as they were in the quattro. After completing the conversion i put 30 litres in and the gauge read full then the fuel light came on after 60 miles so if filled the tank but the gauge is now stuck on empty.

Any clues would be most helpful as nuts and bolts i can cope with wiring not so brilliant

Cheers Dominic