First, follow Art's advice re Fuse 6 problem, I don't what that entails but he's a 240 guru.

re 4) okay, so replace the oil pressure wire, it's degraded and seems connected to the starting system. Get wire that can take high temp, at least 200* +, make a new terminal end for oil pressure sensor, run new wire as long as you can before it disappears into harness with other wires (on a 240 I don't know if that's short or long distance). Splice it in by bare wires and electrical tape or go with butt connectors or even another method someone may suggest...

re 5) I'm still not clear you have the alternator wiring set-up properly. Search here for "alternator rwd wiring" or something like that. Art and others have made some great photos over the years re alternator wiring. Also try *google_images* with "site:brickboard.com alternator wiring" etc...

The car definitely has multiple electrical problems, so keep at it, sounds like to will take some persistence.