Passat: Diagnose Connector Problems & Solutions

Good morning, everyone.

I spent a long time searching for the diagnostic connector on my Passat 35i (year 1991) and eventually found it somewhat by chance under the gear stick. Interestingly, in addition to the black and white connector, there's also a blue connector. Does this connector have any purpose or function, or is it just there so it doesn't end up somewhere else? Or what's its purpose?

The blue stick is for blink codes.

-Uwe-