On my '91 300E, the Front CPS is hard-wired to the diagnostic port on the left fender. No plug. Assuming we're talking about the same thing that is...

Maybe post a pic of the other end as well?

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Currently:
1972 350SL Euro 4spd
1973 BMW R75/5
1981 BMW R80GS
1995 FZJ80 with OM606 Conversion In Progress