According to the electrical manual the switch is wired the same for both model years. You could pull fuses to make sure that the lights are wired correctly. The one thing that you need to ensure is that F11 is 16A and still controls the fog lamps. My guess is that if you swap the connectors at the lamps your fog lamps will only work when the brights are on. If this is the case, then the best bet is to try to figure out why the wiring is off. I've never had one out, but if you can get to the connector (C106) then you should be able to figure this all out. It appears from your description that pins 2 and 3 of the connector were swapped somehow.

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)