Reference pages 4-5 and 4-6 of engine operators manual. If the aircraft in question ran out of voltage, then perhaps it was miswired. Some operators try to handle the logic of the system with key switch and relays. Rotax recommends mil spec toggle switches - seven of them (ECU A and B, pumps 1 and 2, start power, emergency power and start).
Start power ties the two alternators and battery together and powers ECU and fuel pumps until alternators take over. You open that after start because then if the engine stops, the fuel pumps stop - which you definitely want to happen..
Similarly emergency power connects ECU and pumps to battery. That should also be normally open, else you won’t know if the alternators fail, - until you run out of battery.