G'day
Don't have a manual, but if it is the wiring of the plugs you want, that is detailed in the Ducato Handbook available on the Web. Do a search on this Forum for the link. I downloaded it on 7 Sept 2009 so its on a recent Thread here.
Is the user manual you are after for the Blaupunkt CD radio that Fiat fits as OEM in the Ducato (Fiat Ducato CD High) as in the attached pic which as far as I know is still fitted to the X250 models. I believe there were some other brands/models fitted as well.
See their website as well - http://www.blaupunkt.com/de/7640377316_main.asp
Finally here is the PDF of the Ducato Blaupunkt CD Radio user manual that I had scanned & forgot to compile into one file & complete, it is only the second half of the manual concerning the CD version as I didn't think the cassette part would be relevent now. Hope this is of help to those of you who don't have the paper version. Apologies to jep73 for taking so long.
Cheers