Flickering head lights, what am I missing

OK,, the flickering is resolved, the current flow is much more stable, however with the engine running, the rear bumper mounted disconnect no longer kills the engine.
The motor continues to run with the battery disconnect switched to off.
I believe that is because, the way it is wired now the out put from the alternator feeds directly to the field wire and keeps it hot.

If I revert back to the original wiring scheme where I have the alternator field wire running the length of the car back to the rear bumper mounted 4 post disconnect switch, what gauge wire is recommended?
and / or
I am open to other solutions
Thanks