IceLink Plus + E39 Navi/TV No sound

I'm trying to install IceLink Plus on my E39 Touring (1999). It has a Professional RDS Cassette player with 4:3 Navi+TV.
I can control the iPod with the radio (and steering wheel) controls and
can see song titles on the Navi screen, but I can't hear any sound.
The iPod in question works well in another car (with a Business player), so it should not be the problem.
My guess is that the white audio cable is connected to the wrong pin...?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.