i know nothing about the motobecanes..
but one of a magneto's internal coils is usually tapped .. that is, somewhere near the middle of the coil of wire, they attach another wire.
Since the number of turns of wire in a coil determines voltage output, a single tapped coil can output many voltages simultaneously. These "taps" then power devices that require different voltages. So, one section of a tapped coil could be shorted / burned out, while the other sections are OK.