This still doesn’t answer the question though about why the flow of electricity is going all the way to the spark plugs... 
I think it might do this even if I bypass the switch.
Honda 1977 CB750K
I thought I answered this question in reply #19.
The Dyna S powers up in on mode, providing power to and charging the coils. A coil will spark with a rapid increase in power applied or with power removed. That's the nature of coils, essentially a transformer, stepping up the applied power. The secondary twitches with power applied or power dumped. Usually the dump (timed trigger) is faster than the rise of power applied. But, with 3 ohm coils, the input current is far more spikey at turn on. Sudden voltage at the spark tips creates an arc. It could also do this upon power turn off.
Cheers,