7 msd spark help please

the duster we picked up has a 7 msd 7220 box i got a new blaster 3 coil for it
i understand it need's a least 12v to produce a spark with the battery full charge 12.6,12.6 at relay 12.6 at box go to crank no spark thinking that it must below 12 v when cranking, i then boost with another car it get's good volt's spark's & run's (battery is in the trunk) how do i get the volt's i need to get it to spark.
note i'm sure there was a capacitor in the engine bay after 4 year's i've forgot where it was or what it was hooked up to
could this be part of the combo if so i have no idea how it would be hooked up
if not what would it be there & used for i'll try to put a pic of the cap.
thank's newbe