You have found the area of the problem.
One "work around is to pull ALL load off the dark blue, that is cut it before it gets to the bulkhead resistor, and use it to fire a good quality relay, then use the relay to supply ignition and regulator loads
Otherwise, you need to dig in and see where you've "lost" it
Again, the top suspects are the bulkhead connector itself (At least two, the main battery feed goin "in" and the dark blue coming back "out"), the ignition switch connector or the switch itself.