Electrical help needed

Hello, I have studied TONS of threads on the topic, but none have the exact issue im having. Hopefully the experts can chime in...
64 Barracuda, purchased as a shell. Installed new motor, electronic MP kit, later model voltage regualtor and2 field alternator.
My problem is, only 5V to posative side of coil. I ran a jumper to straight 12v and it starts right up. If I pull jumper off, immediately dies. I have double checked ballast wiring, ECU wiring, all seems to be per diagram instructions.
I must be overlooking something simple, but short of spending another 300 on a standalone MSD box. I should be able to make this work.
Any leads on where to start??
Appreciate any help...