I know it works, but never understood how: Batt/Alt/Start

[Tom Endy]

An easy way to think about it, is in a DC circuit when there are two sources of power connected, the source with the higher voltage will assume the load. The battery is at 6.3 volts. The generator (or alternator) puts out a higher voltage and takes over the electrical load. It sees the battery as another load and sends current to it, which charges it up.

it works the same with a positive ground. Current is still flowing in the same direction, only with a different ground reference.

Tom Endy