I have the same problem on a 1994 E320, but no clue how to diagnose the problem. Any ideas what route I should take to hunt down the problem?
I opened the panel below the steering wheel. I was trying to take out the motor and see if it recieves any voltage or if it works at all by giving it power but it looks like it's going to be a whole day's worth of work to get it out.

By the way I am going to take apart the steering column if all else fails, does anyone have directions on how to take it out?