I've converted my '68 points distributor to a Pertronix Ignitor. It works fine with the stock coil, and my car does not have a ballast resistor. I got an MSD Blaster2 coil to replace the stock one now (regular 12v coil), and it came with a ballast resistor to use with points ignitions. Since it's a pertronix setup, do I still need to use the ballast resistor? And what is the reason for a ballast resistor?