What can cause a coil to fail?
In a word, heat. The old-style cylindrical, oil-filled coils (as mated to Kettering and early electronic systems) would withstand pretty much anything so long as they were protected from vibration. You could easily subject them to the sort of electrical abuse that will kill modern “potted” solid-state coils. Once the igniter (or points) breaks the current from the battery and 20,000 volts are created on the high-tension side, it cannot simply die where it is. It HAS to go someplace. Specifically, this means that the high-tension side (or “secondary side”) of the ignition (rotor, cap, wires and plugs) MUST be in sufficiently good condition to allow that current to travel to the spark plugs and jump the gap there. The entire ignition system and all its parts are designed with no other purpose than to strike an arc across the spark plugs’ electrodes, allowing the electrical energy to be dispersed in the sparking action. Now what happens if the current can’t go to the spark plug gap? What
