I agree from what you have posted, it sounds like the column switch. I have never removed or taken one apart.
If it were my car I would put a test light at the pump connectors and confirm that when I use the washer stalk switch it doesn't work. From there, I would try tracing the wiring back from the pump to the switch.
Have you tried doing a search on this site regarding this problem?
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)