[DeTomaso] Why Do We (sometimes) Have Ballast Resistors?

[SOBill at aol.com]

The battery voltage when, cranking the engine can drop as low as 8  volts 
in cold weather. The ignition system must be able to fire the plugs  with 
only 8V across the coil.
 
With a system using ignition points, the coil primary  winding would have 
8V during cranking and 12V to 14V with the engine  running. 12V to 14V would 
cause the coil primary winding, designed to operate on  8V, to overheat 
during a long drive on a hot day.
 
The satisfy these requirements, a resistor is inserted in the  coil primary 
circuit to reduce the coil voltage to 8V volts when the engine is  running. 
The resistor must be bypassed when starting the  engine.
 
The Orange wire on the small right hand terminal of the OEM Pantera  
starter solenoid on the passenger side of the firewall goes directly to the OEM  
coil positive terminal and provides full battery voltage to the coil,  
bypassing the ballast resistor, when the engine is cranking.
 
Aftermarket ignition boxes need to operate on 8V because this may  be all 
the voltage available from the battery during engine  cranking. The need for 
ballast resistors with aftermarket ignitions is  completely up to how the 
circuit designer interfaces to the coil. Some  use ballasts, some don't.
 
Have fun  today,

sobill at aol.com