you say you've changed the fuel injection relay twice but have you checked the engine fuse box for any blown fuses blown?
This is just an idea and whether haynes is right or not as i've found in the past some info in there is really misleading but anyway
According to the wiring diagram (attached) the live (brown) to the pump is fed first from the ECU to the lambda sensor and then onto the engine fusebox, a blue wire feeds onto the fuel pump from engine fuse box, see the diagram for further details, i'd say its worth checking out this area to see if there's any blown fuses and also check to see if you've got any fraying wires that maybe short-circuiting it hope this helps abit: