power supply wiring external to the engine driven part
If that is your understanding you have either visited the wrong forum or read incorrectly.
On the "back" side of the 912/914 there is a flywheel carrying a magnet - or several, I'm not sure there. The magnet passes under a total of 11 pickup coils, producing a gust of power in each at every revolution.
4 coils drive the 4 spark plugs of the one ignition box, providing both timing information and power
4 more coils do the same for the second box
2 coils supply power to the charging circuit
the last coil gives tachometer information
At least this is my understanding, I'll be glad to learn better if I missed something. But there certainly is (or needs to be) no connection between the ignition system and the battery power circuit.
For as much as I heard, there are not often any issues with the wiring. The ignition boxes OTOH have a poor reputation, coming from motorbike maker Ducati. There must be alternative makes but I failed to find any information, up till now. Looking frantically though, as said the Ducati boxes have poor reputation and are quite expensive - for a microlighter's purse, at least.