1971 Mercedes 250 CE with D Jetronic.

Hi everyone, my name is Steve, i am helping a friend restore a 1971 Merc 250 CE. We have rebuilt the engine and are now trying to get the D Jetronic to work.
We have checked continuity from the ECU to all components and all good. We have no power to the injectors, trigger points are ok and returning around 5V to ECU.
We have 12v to ECU pin 16 and 12v to pin 24 injectors. Suspected fault in ECU. We have purchased a used unit that we were assured was ok but same fault prevails. Can anyone give us a direction to go or could the replacement ECU be faulty also. Any help appreciated, Steve.