Turning key to "run" causes all power loss.

The new 8AWG wiring is in, along with a 40A in-line maxi-style fuse. A punched a hole in the firewall near the existing pass-through for the hood release cable and used a grommet to secure the wire. The wire terminated at the ammeter. The old cable was removed from under the hood and all the wiring received new wrapping. She started right up after all of that was done.

However, while buttoning up the dash and ignition switch wires, I found that the car would stall if the connector was bumped. Obviously, that's another loose connection. The black wire (from the ignition switch to the alternator) was also warm at the connector. I performed another voltage drop test and the hot side of the connector (red wire) was 0.35V drop from the battery, so I depinned the connector and tried to clean it and reinstall it. The voltage drop at the black wire was the same, so I started with the red wire first. The stalling issue was still there, so I simple cut the wire and added a single-line connector to the red wire and the black wire. The voltage drop went away, but the car would still stall if the connector was touched just right. Next, the brown wire was cut and a single-line connection was made. The stall issue was still there, which didn't make much sense to me, since the black and brown wires are the current-carrying wires while in the "run" position. And since I was already halfway to removing the entire 8-pin connector array, I just cut the remainder of the wires and added new connectors. My stalling issue is gone, but the wiring is a bit less tidy.