ECU PROBLEMS

I've noticed on this site and on another, plus from personel experience that there seems to be a common problem with ecu's, usually when someone has discovered their fuel pump relay has gone down, once replaced it seems the one wire that goes from ecu to relay has stopped sending a current to it, this has been confirmed by use of another ecu. So why is this, but more importantly can it be repaired easily ??? Some part of the circuit that sends this voltage to the relay must be blowing. I spoke to a couple of firms who repair ecu's and they estimate £150 to repair, but surely it can't be that difficult, does anyone else know of this, do you know someone who is shit hot with repairing these things, do you know the fault,can anyone here do it, got the answers ???? please let me know. I think it could be of benefit to all at some time or other, Many thanks, Smithy, I.O.M