Resistor Unit / Coil Resistor 6 Volt System

[denns1989]

Greetings Again

I searched & didn't find a clear answer for my current inquiry.

My car with a 1949 - 53 8BA 6 volt pos ground system didn't have a "resistor unit" as it's called in the manual or "coil resistor" as it is often referred to... I have rewired the car & just wanted to ask a couple questions.

I'm aware of the general rule that a 1.3 ohm coil is used on a 6 V system, however they were also used on 12 V system with a "ballast resistor" or you can use a 3 ohm coil direct on a 12 V system.

I think I understand that the coil resistor was designed to supply a full 6 volts when cold & then drop the voltage to roughly 4 volts so not to damage the ignition system? But why only on Fords when most other 6 V systems use a 1.3 ohm direct ?

My car had a "1.3ohm" coil without a "coil resistor" & I have to assume it worked, is the "coil resistor" only required when using an original coil that has a different internal resistance ?

I can just order a coil resistor & "original" coil but I wanted to understand if this is only necessary when using an "original coil" for the car or can you just use a standard 1.3 ohm coil & forget the coil resistor... if I upgrade to Petronix, they state to use on "non ballasted" systems with stock coil (not high voltage)... so once again I would assume this means with no "coil resistor"

Hope I'm making sense, thanks in advance