slant 6 ignition problem !!
THIS one could be trouble.
How does the harness appear, look over what you can see, under the hood, flashlight under the dash, examine the bulkhead connector
Look for melted spots
Feel up under the dash with your hand, feel for the ammeter connections, are they loose?
What does / does not work?
Do head/ tail lights work OK?
Turn switch to accessory, does heater blower, radio work?
(Don't push this, if you see or smell smoke, turn it off and unhook battery)
You have a shop manual or wiring diagrams?
First thing I'd do after looking over harness for damage, is pull apart the bulkhead connector and examine that.
There are a few circuits in the car THAT ARE NOT FUSED
The big wires from the battery and alternator are not fused except for a fuse line
The big supply wire to the ignition switch and headlight switch is not fused. Their only protection is the main fuse link
NOTHING coming OUT of the ignition switch is fused, except the feed going TO the fuse box, and of course from there you have fuses
You have the dark blue ignition buss, feeds ignition and regulator, NOT fused
You have the brown coil resistor bypass from igniton switch, NOT fused
You have the yellow "start" wire feeding to the start relay NOT fused.
THE LAST would be something to check. Because you say it cranked "with no key" it's possible that the relay has corroded, stuck or even disintegrated internally. So it may have welded the contacts shut somehow and shorted the yellow start wire to ground.
I'd be looking at the start relay. You can get them open. Take a screwdriver/ side cutters and bend the tabs out and pull the guts out of the can.