I understand what you are getting at. No, you can not use both hot wires off the magneto as the + side connection, and ground on frame. The 2 hot wires are technically two different ends of the same wire that is wrapped around a coil. As the mag turns, it charges the coil, connecting the two together is a no-no.
P.S. hooking to two seperate batteries like this would double amps and voltage. doing it to a coil will not, because both wires share the same source.

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