I've been researching the pinouts for my 1997 A6 Sedan so I can install a Phatnoise box. The Phatnoise does not support the stock Delta CC radio so I bought a Concert I head unit on eBay and replaced the Delta. See my Concert I install Here.
Not wanting to rip the car apart to replace the changer harness, I've decided to make an adapter that will allow me to plug a standard Phatnoise 13-pin Audi cable into the factory C4 8-pin harness. You could do it differently, cut off the connectors and solder the Phatnoise adapter cable directly to the harness in the trunk. I didn't want to cut the harness but that's just me.
The C4 A6 CD changer harness pinouts are not documented anywhere that I could find so I did a continuity check from the head unit end of my harness to the 8-pin DIN connector in the trunk.
The radio connector is as seen facing the rear of the radio. The 96 A6 8-pin female connector and the 99 A4 13-pin male are shown above facing the end of the open connector.
Pins 13, 14, 15 on the Delta CC have different functions than the Concert I. The rest of the pins are the same. The C4 CD changer won't work with the Concert I.
To make the adapter, the 8-pin DIN connectors are available from http://www.mpja.com/listitems.asp?dept=95&main=83&type=1 and the 13-pin connectors from http://www.cablesandconnectors.com/26500-26.HTM.
How to make the adapter cable is still an issue. The data and audio wires have copper shielding. I'll have to find the right kind of wire. On the other hand, I may just pull the CD changer harness from an A6 in a salvage yard.
Notice that the 8-pin connector has no pin for the Data Ground. The shielding on the DI and CLOCK lines is grounded to the head unit chassis but won't be carried across the 8-pin connector to the Phatnoise chassis. I don't think this will be an issue if I provide a good chassis ground to the Phatnoise box. We'll see.
Making the Adapter
Here's the end of the 99 A4 CDC harness with the wires exposed.
They need to be connected to the 8-pin DIN male connector this way. The color of the wires in the A4 harness are given.
This is the tedious part. Getting all the wires cut to the same length, positioned, soldered and covered. Takes decent soldering skills.
And here's the finished adapter. On the left is the 8-pin DIN that connects to the harness in the trunk. On the right is the 13-pin DIN that connects to the Phatnoise cable.
In my sedan, the CD changer harness is located in the trunk behind the right side trim material. It was zip-tied to the gas filler bracket. In my Avant, the harness is on the left side inside the storage compartment.
I plugged my adapter into the harness in the trunk. Then I plugged the Phatnoise cable into my adapter and into the Phatbox.
Now for the smoke test. Ignition on, radio on, press Mode, wait a few seconds, bingo...voice from the Phatnoise comes over the speakers. I didn't have to configure for my Concert radio head. Apparently, the previous owner had already configured the Phatbox for the right radio.
I've been enjoying the music for a few weeks now. The quality of sound is excellent. My method of grounding works just fine. I figured out how to set general random mode so songs are selected from everything on the hard disk. Over 1600 tracks and counting.