4 pin vs 5 pin?

Came across a thread on google regarding the 4 pin ecu vs the 5 pin, and something about dual ballast resistors having a different resistance level depending on whether its being used on the primary side or secondary? I've been having issues with wiring up an electronic ign for awhile and i'm wondering if it has something to do with this... currently using a 4 pin box and dual ballast but until today I had no idea about the primary side and such on that ballast, so its untelling what side i've had it hooked to and all. I also have no idea what that 5th pin would be used for, that particular thread didnt make much sense to me, my plug does have the 5th wire. TIA