Understanding ignition wiring on my 1970 Dart

I think what you REALLY DID is that you have a loose connection somewhere and when you pulled that connector off, you also "jiggled" the loose connection a bit and thought that the dash connector is the problem.

I would do this:

Check where IGN1 / dark blue "ignition run" goes through the bulkhead and CHECK THAT TERMINAL for loose/ corrosion/ burned and wire connections.

Then run down that splice and see if IT failed.

What have you checked?

Another way is "when" the engine has just died, go to the "usual suspects" and check for voltage.....

Check at the ignition switch connector where the blue comes through, check BOTH sides of the connector halves. Check the engine side of the bulkhead connector and if that is dead, check where it goes through the interior side.

And check the splice itself