Relays. The switch you push energizes a relay which energizes the motor.
The relays are interchangeable so switch them around and you may find
the bad one(s). The task is to find where they are clustered.

You may have a bad fuse in the fusebox of the vehicle.  Your pattern
fits the pattern of the fuses.  One fuse protects the driver's window
and the right rear, another the passenger side window and the left
rear.  I had a fuse with an invisibly small crack once and I took it
to the dealer and as soon as the mechanic saw that my passenger front
and rear left were out he told me to check the fuse and that is what
it turned out to be.

Those switches do go out from time to time though.  They aren't
terribly expensive and are readily available from on-line parts
places.

Prices on switches vary from $11 - $22 here:

http://www.autohausaz.com/search/product.aspx?sid=lsvv5o55szndphfckfnwlrv3&makei
d=800016@Mercedes&modelid=1194319@300TDT&year=1982&cid=window@window&gid=4624@Po
wer%20Window%20Switch

You can get both sides for about $45 total.

I don't like to contradict Mr. Lambach because he is both
knowledgeable and very helpful, but on my 1982 300 TDT at least, I
don't think there are any relays in the system, at least I have never
seen one and my mechanic at the dealership told me there weren't any
when he pointed me to the blown fuse.

I would start out with fuse first... take them out and put a new one in.
They look okay in place but when you take them out... you will see they are
bad.

If that didn't work, then I would take the switch apart and clean all the
contacts inside it. It is almost always the switch when you can open but not
close... or vice versa.

Hi
You may disconnect the battery for 10 mins and reconnect it again.
Good luck
Chris