Percolation? Heat soak? Don't drive during summer??

DentalDart said
It was connected to the negative post on the coil. I disconnected to see if that is what was causing the coil to fire prematurely. Which it was.
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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.