Since I couldn't find all the information needed to make this work in one location: Here is everything with pictures when I installed a Kenwood unit today.
The stock Bose system uses an amp that is then splitting front and rear for the speakers. There are only 4 wires from the stock radio going out: Lpositive | Lnegative and : Rpositive | Rnegative. There is no distinction between the wires until they run through the amp which then splits them between front and back.
Unless you are rewiring the entire system you will only need the one set of stock output wires from the aftermarket radio or use the pre-amp RCA outputs if you radio comes with them. I test wired everything together and use the regular speaker wires instead of the pre-amp RCA outputs.The first three pictures are not mine so credit goes out to MB and whoever made the third one. I can remove them and make my own but figured to just use and post them instead of reinventing the wheel.
This shows the location of the audio system components.
Beside the connection for the B part the above is correct.
This is the wiring approach I ended up using.
Insert the radio removal tools on the bottom left and right. The above shows the clips that will be disengaged with the clips.
another blurry clip picture
the connections on the stock bose radio: power and phone cables, optical cd changer cable and the antenna cable from left to right
close up of the stock 2 piece wiring connectors 2x5 and 4x4
the two pieces of scosche stuff you need to get: antenna adapter VWAB and VW01B Wiring harness
the VW01B wiring harness has two connectors that need to be switched: the red and yellow
each connector wire is held in the plastic harness with a small bend metal piece, use a very small screwdriver or bend paperclip and push in on the clip and push the connector out.
this picture shows how the red and yellow wire had been swapped. their are constant 12V and switched 12V by the way
old radio with the adapter harness. in the background you can see the "dentist" tool i use to play with the pin wiring.
another look at the stock harness adapter prior to removal of the excess wires.
this is the stock mercedes connection you will connect to.
once everything is cleaned up and your connector should look like this:
the 4 greyish wires are the speakers and the bottom row is the power connection stuff.
The pink wire is for the phone which I ended up removing as well.
now comes the time where you connect everything and TEST the setup prior to soldering to make sure everything works!!!
twist and solder all the wires together and then use heatshrink around the connections for a clean install
ziptie the adapter harness and the aftermarket radios wires together to keep clutter to a minimum.
use the VWAB adapter and push that into the stock antenna cable
push the old not used fiber and telephone wiring out of the way
connect everything up and enjoy a new radio.
I had the options in the radio to change the speaker output voltages and dB so I had no issues with crackling or popping as some of the other people reported in their threads. Volume works fine and doesnt sound distorted under loud music either.