You seem to have the gist of it now Dave. MMC provisioned for the optional front fog or driving lamps to be plug and play. Don't have any pics of dash wiring or even where the optional switch is supposed to fit (is it one of the group of four between dials?) but hopefully Rog with his similar age +4 can help here.
The wiring schematics I refer to elicit quite a lot of info if you know where to look. To this end I can tell you the switch connector you are looking for routes out of the chassis loom at the same point as its multiway dash connector but with 400mm long wires (red/orange and blue/yellow), so probably cable tied out of the way whilst unused. You may be able to see it from under the dash, but again Rog may be able to help.
If you have difficulty sourcing the correct switch to match connector, any single pole on/off switch will suffice and you could connect direct to the two wires after chopping off connector. Pardon me for stating the obvious but disconnect battery before dropping dash.
