sorry for the highly technical lingo there....but im curious about something....in my 300SD, theres a round wiring harness with a lot of female pins in it...its located somewhat close to the glow plug relay on the drivers side fenderwell...it has a round cap on it that is attached with a little plastic peice...it looks to me where you might hook up some sort of diagnostic tool...but if thats the case, what would it check?

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction

It is the diagnostic dock, as you thought. On top of the tach amp.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)