First DVI connection has failed, as I said a few posts ago. Here again a picture of the DVI connector:

By Ionuion at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4379981

Also on Wikipedia is noted that single link DVI works up to 1920 × 1200, only after that the second link is activated. I figured the shielding isn't very much needed and the GND can be wired on a more convenient location

It works! With only 13 wires. I knew the DDC cables were correct because I had used them for VGA, but still it was a surprise that I didn't make a mistake. :)