My installer fixed the mixup. The leads from the wheel to the adapter were crossed.

The remaining problem is more difficult to tackle, though. Some of the buttons just don't emit anything (as viewed by hijack's Button Display). One button just never works, two others sometimes work (mostly not, though).

My installer was kind enough to temporarily fit a Sony CDX-M9900, and it just worked perfectly.

So maybe Sony did change its protocol? Or my original tuner is broken?

Thanks,
Pim