Good morning Kirk, NOT to be argumentative (ONLY here to help) but try and educate some here who may be confused by the terms "internal ballast" "internal resistor" or "internally ballasted" , let me comment on your statement
"The 12V coil has an internal resistor"
Actually if you take "most" typical old farm tractor 12 volt coils and disect them and/or x ray to look inside, YOU WILL NOTTTTTTT FIND A DISCRETE STAND ALONE "RESISTOR" TUCKED AWAY SOMEWHERE INSIDE THE CAN... Their necessary (around 2.5 to under 4 ohms typical 3) primary coil winding resistance is achieved EITHER by more windings/length and/or higher resistance wire NOTTTTTTTTT by adding a stand alone discrete "resistor" in series with the primary windings in order to reduce current and/or reduce voltage across the actual primary coils of wire........
Its true some eaqly autos indeed did have a coil with a seperate porition of the can for a true stand alone discrete resistor and many had like a ring or seperation around the coil for the internal actual resistor
Allllll wire (NOT a prefect zero ohms conductor) contains "resistANCE" but wire is generally called WIRE NOT A RESISTOR at least in engineering and technical circles. Wire while it has some resistnce is very low resistance while a "resistor" is purposely designed for higher then straight normal low resistance wire i.e., it may be 1 to several thousand OHMS, its called a "resistor" NOT wire (although some resistors are wire wound with resistive wire and called wirewound resistors)
Sooooooo "most" typical old stock 12 volt farm tractor coils called internally ballasted DO NOT HAVE A STAND ALONE DISCRETE "RESISTOR" TUCKED AWAY SOMEWHERE INSIDE THE CAN. Their primary total resistance (made up of allllllll those windings/turns of "wire") is around 2.5 to under 4 ohms if a 12 volt rated coil and more like 1.25 to 2 or so if a 6 volt coil
Make sense?? Hope this helps God Bless n take care
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