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.

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.