Stright up is off.
Left is headlamp, tail lights, dash lights(no bib lights) lic plate light.
far left is parking(bib), tail lights, plate, dash.
Right is tail and plate only(for convoy use?)
You can re-wire(from back of switch, with a jumper) so that when left(headlights ect) the bib lights will come on, I did this on my 67 fj45.........I just think it looks better and is prolly safer with the bib lights on with headlights, also less chance a cop will pull you over for having light not working........even though on 60's vintage rigs they are not required.........but how many cops are gonna know that?
Yes its a wierd set up and I can see why you suspect the PO re-wired but I bet your is correct....