Hi guys,
The electric #4 pump can ONLY be operated from the:
*** #1 external power side, or
*** #1 APU power side.
So, if you get an MEL that the #1 generator on the APU is inoperative, you cannot pushback using the #4 electric pump, you will have to use the #4 ADP!
Cheers
and, hi '18-Wheeler' - how are ya!