Turbo 383 in a A-body Barracuda

Ok, wish I was there. It would be easier to diagnose. Im trying......

So you wired it like the first picture I posted. So it is + triggered off your ignition switch at cranking.... I would check that wire when cranking again. I bet it shuts down and looses +12V.

Where are you pulling the MAIN + and Neg leads from?

You are either loosing power or ground, I doubt it's the 6al.