I do remember some confusion 10 years ago on my Pertronix conversion. It was not clear to me if I should use the ballast resister or not, and which of three coil possibilitys I should use. I must have made the right choices--No ballast and not sure which of the two Pertronix coils I used. 100% satisfied with it. .I am thinking of using the Pertronix 3 on my 64 Dodge big block build.. I just wonder if it will deliver what the advertising hype claims.....................................MO