Originally Posted by Henn28

The car has a large number of grounds. The engine harness is grounded at several places, if I recall correctly. Including at the heads (v8, not sure about the 6 cyl), and at the electronics box on the right side of the car, up under the cowl by the windshield. This is where the harness terminates and where you will find the DME, transmission ecu, relays etc.

I think the point was/is that your injector issues are a symptom, not the real problem. Do you have the Bentley manual for the e53? Invaluable for serious work on these things.