To make a long story short, I had a real
tough time finding my '94 E320 CD changer
cable. I bought a MB changer from MB parts
and I had to get MB service to tell me it
is in the right hand side under the cover
near the wheel well.
It is not the left side cable for the
celluar phone. (The service foreman was
really mad that parts sold the changer w/o installation. I did not want to pay $200
installation for a CD ready car.)
BTW for the extra $100 or so, I think
its better to get the MB one to avoid
the hassle of getting the wrong adaptor.

Good luck.