[Flathead Fever]

Here is another thought. There is 12.6V at the ballast resister when the engine is not running but there is 14.2V when the alternator is charging. 12.6V divided by 3 ohms is 4.2 amps. 14.2V divided by 3 ohms 4.75 amps. As voltage goes up amperage goes up. If the the system was overcharging at 15.0V divided by 3 ohms that would be 5 amps. That might cause enough extra heat to burn up the ballast resister. That's one of those things that happened once or twice to me in 30-year's.