A point on the "a coil will only fire at a higher voltage. . . " thing.
In all my years of being around electronics, the coils and transformers I worked with were designed for a set voltage. Though that could vary under certain conditions, if a coil was firing at a higher/lower voltage than the original circuit was designed to fire at, it meant something was wrong.
For example, coils work by fighting change. Using a points system example, as the points open, cutting power to the coil, the coil voltage keeps raising, until the voltage can no longer jump the point gap, and until the output voltage can jump the gap of the plug.
For a good running rig, this would happen when the rotor and terminal on the cap are perfectly aligned.
Now, consider my old 97 Astro, or my 01 Accord. Both started eating rotors and caps in a fraction of the miles they did when the rigs were newer.
It was discovered the distributor gears on these rigs wore, going from nice, square teeth to something you could cut a steak with (literally). This problem was repeatedly reported on the Net, but no one explained the "whys and wherefores."
SIDE NOTE: This is, likely, a more common problem than most realize, and justification for a distributor swap a few tens of thousands of miles down the road.
Obviously, sloppy teeth allowed/caused the system to fire at other than during perfect alignment of the rotor and cap terminal. Mindful of this, I remembered what I noted above - coils fight change, which results in the coil output voltage climbing, until the voltage can jump the sparkplug gap, or someplace else in the system, if there are problems.
Since the gap between rotor cap contact and rotor grew, just as with the much lower voltage and amperage points, the voltage grew in the coil, to not only get past the plug gap, but the gap between the distributor contact and roter too. This caused a lot of premature wear on the cap and rotor.
In the end, the coil was firing at a much higher voltage than the system was designed for. It could well have been 10k more than stock.
Even with new, quality plug wires, I could see an aura (which is when all the foregoing (coil voltage raised higher than normal) occurred to me). The quality plug wire dielectric strength was inadequate in relation to the higher voltage from the coil, caused by the fire gap in the distributor rotor and cap.
Upon pulling the distributors and considering the condition of the teeth, compared to photos of new gears, that the distributor firing point had changed over time became obvious.
The new, fairly inexpensive distributors solved all problems, and the rigs went years before needing new caps and rotors.
SIDE NOTE: In light of the abuse the coils took (I could see a bit of aurora thing around the Honda coil), they got changed along with the distributors.
