The entire purpose of resistor wire with a regular coil is the same as a any other regular ignition system using a coil + "ballast" resistor.
Regular running places a series resistor in the DC power connection. During cranking, when battery voltage can be fairly low but still sufficient to turn the engine quick enough to start it, the available battery voltage may not be sufficient to produce a hot enough spark to start the engine.
So, a lower voltage coil (6v) is used with a series (voltage dropping resistor) AKA "Ballast" resistor (or resistor wire)
During cranking, when turning the "key" to the start position that series resistor is switched-out ("shorted across") or bypassed while cranking applying available battery voltage to the coil to produce a hot enough spark to ensure starting.
You could use most 6v coils with 12v but because the coil primary winding current would be high (double) they would run much hotter and many would eventually fail.
The more modern electronic systems will operate from 8 to around 24v and still produce adequate spark.
The Delco EST doesn't use or need a resistor. If you suspect resistor wire in your system you need to check and locate it so you can remove it........................... the following FAQ outlines a procedure.
http://www.ebasicpower.com/faq/delcoestwiring.htm
Cheers,
Rick
Let me also add, if the original ignition system is removed or disconnected, you cannot check for resistor wire by simply measuring voltage if that primary wire is not connected to something drawing current.
It will still show supply voltage (the volt meter doesn't draw enough current through the resistor to produce much of a voltage drop)
In that event, you must place some sort of "load" on the IGN power wire
(a light bulb works great if it draws 4 or 5 amps etc .......tail-light, stop-light , even a small headlamp etc)