kev90spec3i

please help me im new on here and hope someone can shed some light on this. i broke down in my xr3i 90 spec efi, after first thinking that the fuel pump was knackered in the tank i stripped it down and tested it and found out it was working fine and the relay was switching fine. traced the problem to a fault on a black box mounted on the sender unit where the power and earth goes into it but it is dead going out of it towards the pump. the sender also has 2 plugs plugged into it and all the ones i have located are differnt with only 1 plug. Can anyone tell me if this black box can be bipassed or if any other sender unit / pump will fit. PLEASE