..... I took a wire and ran it from the batteries to a spare fuel pump i have and got fuel to the injector pump, only to discover the injector pump is not working properly. ....Ant
Can you provide a few more details as to why the IP isn't working properly? Was the fuel flow rate good with no air? Did you verify that the fuel system was 100% bled? Did you check for return fuel? Did you crack lines at injectors & found no flow while cranking? Just trying to ascertain that you've done the basics before you spend a bunch of money.
Edit--WRT fuel pumps not running, I'm assuming you've checked the other basic things like DC fuse, TM check on BS switch & also on Start/Stop/Run Switch. Also do you get the fault indicator lights OK? Last question--do you have a known good or spare MEP-004A nearby? If so, swap out the wiring harness to the control cubicle with the one from the working unit. If you don't have a spare, remove this harness & check for corrosion on the amphenol/cannon pins/sleeves, use contact cleaner & re-connect harness. I had the opposite problem as yours (fuel pumps running all the time) & found a short somewhere on the wiring harness.
Looking through the TM you can locate the following components that may or may not be relevant to the fuel pump problem:
L1--Engine fuel solenoid
L2--Day Tank solenoid
K1--Stop/Run Relay
K8--Fuel Level Relay
FL1--Fuel level (float switch)
FL2--Fuel level (float switch)
CR6--Fuel pump diode
TM has testing info for these components.
Kevin