[napa68]

As the risk of being that guy who has not read the thread in detail and repeating something you have done or was suggested....................have you monitored the voltage coming into the ballast resistor?

It is possible the circuit is getting heated up and dropping voltage. Just a thought.

I can appreciate your frustration. The problem seems so simple in nature (as these are simple cars) but you get so pissed off that you are ready to throw the kitchen sink at it and get away from the basics to diagnose.

My apologies if I have repeated something

Keep you chin up. You do nice work Dave and are a real asset to this site!

Tim