Quote: Let's try some troubleshooting instead of mud slinging.
If your ignition switch is from 1973 we are all wasting out time here as this is classic symptoms of a bad ign switch. OK????
Voltage tests should be done when the car is running.
When the car is running there should be 13.8-14.4 volts across the battery terminals and 7-9 volts at the coil. Period.
Pick a ballast resistor that puts the coil voltage at 9 volts.
The previous ignition switch was about 6 years old and I just replaced it with a brand new one. Voltage drop across the switch is ~0.2V.
With the motor running with fans off, voltage is near 15V and with fans on, drops to around 14.2-14.4V or so. This translates to a volatge on the ignition side of the ballast of ~13.8-14V.
I think you are correct when you say the issue is the ballast. The ballast is only leaving 4.2V on the hi side of the coil once the fans are on. When you put the car in gear and the idle drops to ~700 RPM, the coil voltage starts falling below 4V and thats when the idle starts dying.
I have two ballasts on order with lower resistances. I will measure them when they arrive and fill everyone in on how they work!
