Wiring nightmare! Help

The flickering headlights could be the ground,as said. I think in 69 its on the bumper side of the rad core support,close to the driver's side headlamp bucket.

If the indicators are both on, then there's a good chance all 4 of the signal filaments are also on. It may be that the emergency flasher switch is on, but the flasher is defective. This flasher IIRC should be a 3-prong unit.The electronic flashers work better in this application.The illumined signal indicators could also be problems in the turn-signal switch or the bulkhead disconnect.
Did you at any time smell hot, melting plastic?