I think Steve may be right because I just
replaced the driver side window switch
on my 300D. I tested the old one first
and when I unplugged the center permission
harness, The rear windows did not work.
Also the harness wires were loose because the
bottom clip-on plate of the housing had fallen off.
1.5 cents worth

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1979 300D
133K miles
1989 300SE
1995 C280