I would also measure charging voltage with the engine running. Maybe you are over-charging. At higher than idle RPM, where max output would be high.

"Possible causes are: Faulty charging system (stuck or shorted regulator/alternator)"

Edited Wednesday at 11:41 PM1 day by Zed Head

I just re-ran the voltage drop test and its currently showing around 12 volts with the LED not blocked and I think 1.5 volts when the LED is blocked. I tried driving it around for 20 minutes to force it to fail but all I managed to do is annoy my neighbors by making a lot of noise.

Why are there two ballast resistors? I'm assuming that I have a total resistance of 3.0 ohms with the three terminal resistor providing 1.3 ohms and some fraction of that on the middle terminal.

Possibly change the system to a higher resistance coil? And get rid of one or both ballasts. Just a thought