6. Cylinder duster is now a 340 ignition issues wants to start when you let up on the key

flathead31coupe said

coming off the amp gauge in the dash. There's a red and black wire that go through the firewall in a small grommet. The red goes looks like to a fusible link to the starter relay and the black I believe goes around to that big white connector on the engine

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That is a heavy duty arrangement. Probably the '65 amp' alternator option, either with or without the heated back glass.
If you post photos it will make it easier to narrow down what is on the car.
The 60 and 65 amp alternators will be indicated on the tag if its still there.

Not many of these optioned cars documented. Mostly the ones with the heated back glass but even then not '75s.
Forum member Mark has one in Switzerland but IIRC its a '74. I reminded him to follow up so fairly recent thread.

As a wiring strategy it is pretty straightforward.

The complicated wiring is the seatbelt interlock. One answer would be to wire it so it is always ridden. Same way the switch on the fender temperarily overides it.