Arthur is probably right-on. First, you should only use the spark plugs stated in the MB manual-- not platinum ones (in the opinion of many and not all) and not ones with a 0 on the end of it (as-in W9DC0 instead of W9DC) based on my experience.

Also, you are mixing heat ranges since you said you only replaced 2 of them. So not only did you switch heat ranges, but you also mixed heat ranges. All bad. Even if you fixed the crossed wires or plug wire connections (per Arthur's post) you will still probably have problems.

My 84 380SL is very sensitive to spark plugs. While I have a set of NGK's with no resistance and haven't tried them, I can say that the car runs perfectly with a W9DC, the same plug the car was originally built with. If you put for example a W9DC0 in there, it develops an extreme irregular miss at idle-- the whole car shakes.