Don’t know A320 and B747 fuel circuits , but if like ATR42/72 , putting fuel pump switch on is mandatory .
Fuel pump is used only for starting and when HMU fuel pressure is OK is automaticaly cut off.
A jet pump then feeds engine HMU using return flow from hmu.
Switch must be ON to open the “motive flow” valve , crossfeed valve must be open to feed engine if not .