Bryan, so would you say a coil from the 40's/50's stamped 12V is #3 "rare". I have a box of them, maybe I should sell them on ebay. If I put 6v on them they would not fire, right?

 

The USA made Andover coils I use are over $30
Andover Coils Home

 

I would call it rare if those took the full 12v - they just don't make them that way (much), almost everything uses a ballast resistor. Regardless if they are marked "12v" or not, it is in how the installation instructions tell you to install - few will say "do not use ballast resistor"

 

I just bought one at Carquest that is labeled 12 volt...and..it is clearly printed on the coil not to use a ballast.

I think I would have preferred an external ballast type because the solenoid can provide 12v during starting for a hotter start. It doesn't seem to be much of an issue.

One benefit of the external ballast is that if you ever leave the key "ON" with the engine not running....and the points happen to be closed, the ballast will heat up and increase resistance....that will protect the coil to some degree.

Dan