Did they work at one time, or, are you a new owner, and don't know?

I think there are relays in the electrical box under the hood. You might try swapping some of those around.

The reason is that I had a non functioning passenger seat on my -new to me--1982 300SD. I replaces swicthes and rebuilt switches. I could get the seat motors to work if I applied 12v diesctly to the wires, but not thru the switch. My problem turned out to be a previous "repair" where the "mechanic" mis-wired the switch connection. The switches test OK out of the car, but failed to work in the circut.
The morale is " Never assume anything!"
You could also have a broken wire in the door.
Try applying 12 volts to the motor connections inside the door. Then see is you have voltage at the same connectors. It will soon be obvious where the fault lies. Just be patient, and never assume anything.

__________________
1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags