Charging system voltage high
Blue wire that goes from ignition switch to underhood loses about 1v between ignition switch and components but that wire feeds ballast resistor,control module,goes to voltage regulator and alternator..
THAT IS your big clue and THAT IS the area of the problem.
The path for that wire is from the battery, fuse link, BULKHEAD CONNECTOR (hint hint) to the ammeter circuit, the ignition switch connector, ignition switch, back OUT the ignition switch connector, BACK through the BULKHEAD CONNECTOR, and to the points that it fees, IE ignition, regulator, alternator field, electric choke if used.
One volt is a LOT. Go down the path you started, ---disconnect the ignition from the dark blue and apply a big load, about 5 amps or so.
Then go backwards from the engine bay, check the INSIDE of the bulkhead connector, both the battery feed and the dark blue ignition wire.
Take the bulkhead apart and inspect and clean it.
IF YOU CAN NOT or "will not" fix the problem, one way out is to install a good quality relay, fuse the supply to it, and use the dark blue to do NOTHING but to "key" the relay. Then feed all the loads in the engine bay off the relay contacts
So feed the relay with a good fuse, located away from engine heat, supplied from the starter relay stud. Feed the output from the contacts to your old "dark blue." You'll have to break the dark blue after it comes out of the bulkhead and BEFORE it splits off to alternator, ignition, and regulator.
Wire one coil connection to ground. Wire the other coil connection to your old dark blue coming out of the bulkhead.