OP has said, several times, that it cranks if the RED wire is energized; so I don't suspect the starter/solenoid/relay at all. It's pretty clear Fat Black has no voltage, but does it have continuity to ground? I would like to know about that both ways, with the white 6-pin connector connected to the ignition switch and with it disconnected. I believe the OP has also said attempts to power up the double BLK/WHT wires trips the CB in the power source. What is the rating of that CB? If it is fairly high, like 10-30A, then tripping it indicates a short in the circuits fed by the double BLK/WHT. We probably need a more complete schematic, to start following those wires.