yellow rose said

How does the green wire “fire” the coil prematurely?

It can’t. The trigger, whether it’s points, a light or a magnet fires the coil.

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yellow rose said

That I understand. But the green wire doesn’t actually trigger the firing. The switch (points, light or magnet) does that.


EDIT: a quick thought just popped into my head. I suppose it is possible that a grounded wire can trigger firing. So DD may not be on the wrong track with that. My bad for not thinking that through.

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Phreakish said

Correct. But the positive side of the coil gets ignition voltage, if a poorly routed wire grounds the negative post of the coil and then disconnects the coil will fire.

But you're right, it wasn't causing the "coil to fire prematurely" it was causing the "coil to be constantly energized wit a poor connection resulting in a constant barrage of sparks".

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