I tried to find a wiring diagram for a Mercedes-Benz 129 500SL, but it did not come up with anything in the WIS/ASRA program. But when i used the same search method, but for a W210, it brought up several wiring diagrams.
My 129 500SL:

a screen shot of the search:

I had no trouble printing the wiring diagram using either the icon at top right, or the "file" pull down from menu bar.

In order to produce a pdf, I simply printed to a utility I have on my computer called Cute pdf that shows up in the list of printers and then saved the file to my main Windows 7 desktop, or anywhere else that I chose.

The other thing you might try, is a Full Text Search (instead of Standard search). Put in a couple of words regarding the system you are interested in and do an advanced search. I came up with all sorts of stuff that related to 129 chassis. But did not try to narrow it down.

UPDATE! If you enter the car as a 129 using (chassis Mode, click on all for Major Assemblies (for now). Then click on Table of Contents. A list will appear on lower part of screen that will include wiring diagrams under several sections. Keep clicking and you may find section you need!

Attachment:

Mercedes WIS i used(quality guaranteed)

WIS for free (this expires after i used for a few month)

Hope my methods helps someone in troubles with Mercedes Star diagnosis wis.
This article from mbstartool technical office blog: How to find Benz R129 500SL wiring diagram in WIS/ASRA