On my w210 the problem was the wire into the external junction was corroded and had broken.
How to remove rear door panel on 2000 mercedes e320.
There is a square clip near the lock that secures the door panel to the frame.
Here is how you remove the door panel from the old mercedes e klass from 1997 is very easy it have just tree screws and some plastic clips be very careful n.
Then insert the pliers into the crack between the panel and the frame.
If the door is equipped with an airbag remember to disconnect the battery and remove the screw under the srs decal clip.
Once all the screws are removed the door panel needs to be popped outward by using an upholstry clip tool or equivalent.
Gently pull the door panel out.