Ignition module failures

I can guess a few problems for failure.
1. Spark plug cable, or coil to cap cable intertwined with distributor pickup cable.
2. Intermittent ground at module.
3. No ballast resistor, resulting in high peak current, and main transistor failure. It would also show short on lead that goes to ignition coil (-).

My guess would be 2, loss of ground during ignition event, may result in undesirable path of high voltage, finding ground via pick up coil breakdown to distributor. That event would likely short transistor at pickup +.