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.