As you can see Vinnie, each plug...
... and switch are unique to each other.
I'm unsure also... but possibly for the REAR fog light on some European models... especially for Great Britain. My '79 came with 3 switches and one Rheostat and one BLANK, with one dangling connector that I never did figure what it went to. I did connect it in error once to the E-Flasher and took about 3 weeks to figure out what I did wrong! I didn't know there was more plugs than switches at the time!