What year 300SD ?
The 1983 has wires connected.
I know 85 has plug on connectors, maybe 84 too.

But before that... I just opened and repaired mine with some contact cleaner
and small file (or sandpaper).

To take off the door panel is not hard.

Remove the piece of trim in the window/doorframe.
Lift the door panel out from the door. Earlier Benz use clips
that pop out, you pry the panel away from the door.
Not the 300SD, if you pry or pull it will break the not replaceable clips.
Lift.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250