...what model???

There are several different systems...
Up to late 80's, beginning 90's mercedes had an electrical right side and manual left side mirror.
After that mercedes had both side mirrors electric adjustable. At first mercedes had a 1 switch, 2 power mirror system (both mirrors have a motor to answer your question) and the later models have a combined switch (panel), additional door mounted relays and power mirror system.

I think you have one of early 90's with the separate switch...
What do you mean with the passenger side is the one who is moving...is that the case when the switch is set on driver side?

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)