'66 Barracuda starts then dies right away

On my diagram it looks like the "run" from the ignition switch is dark blue to the bulkhead connector, dark blue with a white tracer to the ballast resistor, then dark blue from the BR to the voltage regulator. And the brown from the ignition switch is "start." Sound about right?
Probably close enough. I'd put the key in RUN and make sure you have voltage at the end of that blue/white wire, the one that comes out of the connector to the ballast resistor, if no voltage try wiggling the wire at the bulkhead connector. If you get juice there, it's a bad connector. If not, probe the contact at the bulkhead connector at that wire's slot for voltage, both under the hood and the dash. If you've got juice under the dash but not under the hood, again bad connection at the bulkhead connector. If you want to confirm the car will run once you track this down, run a jumper from the + batter terminal to the + terminal on the coil. Should start and run no matter what. Its probably time for me to mention that I in no way shape or form are an expert at electrical stuff, I hate it as much as the next guy and know even less. This one, though I spend months tracking down myself before I figured out that help was available.