Check you distributor connector Steve.
I have seen those contacts inside them spread open and not make contact.
If they don't make contact then nothing tells the box to fire the coil.
Since it fires when you turn the key off you know it has power available.
It sparks when you turn the key off and that is what the igntion box does, (shuts the ground to the coil off momentarily to make the coil fire) so that pretty much narrows it down.
