69427 gave an excellent technical description of what is happening and how the ignition works with a ballast resistor. From what I see the disbelieve is in what others have read or understand about the electric description he gave. Try this non believers. Go disconnect the resistor wire or wire from the ballast resistor (depending on your system) from its connection at the coil and measure the voltage with key on. Guess what, it reads 12 volts. Why, because there is no current flowing. A resistor resists or limits current they dont function as a voltage regulator. When connected, then you will measure a reduced voltage when the car isnt running. Why you now ask, for the exact reason as mentioned above in a previous technical response. The result of limiting current is a voltage drop. IT will vary depending on if the engine is off or running.

 

With a resistor wire, if you leave the iginition switch in the "on" position for long, you'll burn up the resistor wire and perhaps other stuff. That's the main reason our cars have an "accessory" position on the ignition switch, to keep that from happening. To verify,..leave the key in the "on" position for a minute or two with the engine off,..then feel how hot the resistor wire is.

 

Yes they are used to regulate voltage. The ballast resistor is a classical example. It may not be the most accurate, but in ceratian situations where the current is known an resistor is installed to drop the voltage. If the current draw is steady, a plain resistor will work great. In this case it has nothing to do with limiting the current, its function is to drop voltage. It does an excellent job in that if the current starts to increase it drops more even more voltage.

 

I just looked though my tech manuals for more info. Here is a quote:

"Ballast Resistor:
The ballast resistor limits the CURRENT buildup in the coil to a level that is safe..... If it wasn't for the ballast resistor, the coil primary CURRENT could easily build to 10 amps wich would blow out the coil in 4 to 10 hours. GM HEI limits this with a special current limiter inside their module. So with GM HEI systems there is no need for an external resistor."

Note the use of current and not voltage. Yes you can use a resistor to drop a fixed voltage to a lower voltage provided the system is steady state which an ignition system is not. I don't disagree with anyone that says the resistor drops the voltage. To what level depends entirely on what is happening downstream of the resistor. The whole point by someone previously has been to state what is actually happening with full technical details to show what purpose the ballast resistor actually serves.

I'm sure many simple texts on this topic will just state it drops the voltage down so components are protected or something to that nature. A simple answer to its purpose so that service people understand that its supposed to be there and gives a reason why not to eliminate it.