Turning key to "run" causes all power loss.

A couple of thoughts on my next steps:
1. Measure the voltage drop across several sections of the wiring, to see if I have a bad connector. Ideally, I'd do this with the engine running (and high current flowing), but I can't start the ol' gal up as-is. I'll check the negative battery to several ground connections (engine, body, etc). I'll check the positive wiring through the starter relay, fusible link, ammeter, etc.
2. Remove either of the 2 ACC or RUN wires from the switch side of the switch connector. If there is a big short somewhere downstream, then disconnecting one or the other of these should help narrow it down. The dark blue wire goes out to the engine bay and powers all of the ignition circuitry. The black wire powers all of the internal items (lights, radio, blower, AC compressor, etc).
3. Get a heavy wire and run it from the battery positive all the way to the black or dark blue switch wires. This will bypass the connections at the starter relay, the fusible link, the bulkhead connector, the ammeter, and the ignition switch. If any one of those is causing the "short" then this bypass wire will allow me to start and run the car.