I could not easily find how to trace the wiring in the CD Manual.
This book has wiring diagrams in it and dose not cost much and is available at local autopart stores.
Haynes 63012 (697)
Mercedes-Benz Diesel 123 Series
1976thru1985 4&5 cyl, 200D,220D, 240TD, 300D, 300CD, 300TD
The info is on pages 291-293 in my book.
They show #27 Relay-I window lifts and #28 Relay-II window lifts.
I am not sure if this means there is 2 styles of relays used or there is more than one relay per vehicle. Also I could not figure out in the short time that I scanned over the wiring diagram how everything was connected to pass that info back to you.
If you can get the car Owner to buy the book for you.
Depending on who you buy the book from the price can be $17-$24. This money might be better spent buying the Factory CD from a Dealer. The one I have covers the same modles as the Haynes manual.
This is a pic of one of my window fuses. It looked good from the front but when I pulled it it was no good.
I wish someone else who knew more about your problem would chime in as I am real weak with electrical stuff.