Instructions for rewiring Audis for Portable Cellphones (was Re: phones upgrades)

[quinn@hns.com]

In response to the recent thread on Cellphone replacement in Audis,  I
found this recent post on A4.org regarding reusing/rewiring/adapting
the existing cellphone wiring in your Audi to use a handsfree unit for
any portable cellphone (in this case it was for an A4, but all Audis
should be similar).  You may want to cut this and store for future
reference (as I did).

The cellphone wiring FAQ he refers to (below) may be found on the
A4.org FAQ pages at http://www.a4.org/faq/faqs/faq63.shtml
(again I think that all pre-wired Audis use the same schematic, but
YMMV and so DO THIS AT YOUR OWN RISK!).

Thanks to "Kevin P" of Cellular Integration (whoever you are) for
this info...

-Mark Quinn
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Posted by Kevin P on August 07, 1998 at 12:41:01:

Since we announced the closure of Cellular Integration, a number of you
have requested that we "share our secrets." Here you go:

The A4 was designed and prewired to accept a standard Motorola car phone
with a handset physically (not electronically)customized for Audi. The
 phone is located in the trunk, plugging into a DB25F data connector
behind the driver side trunk trim panel. The handset goes into the console,

plugging into a RJ45 phone connector that is under a small trim plate.

The DB25F in the trunk is the key to the entire installation. As the only
interface to the factory phone, it has all the signals needed, IN ONE
PLACE. It provides +12VDC (both battery and ignition switched), ground,
microphone, speaker, muting output to the radio, and eight wires that run
to the RJ45 in the console. All this is shown in the 'phone system
schematic' posted in the A4.org FAQ. (Note: the RJ45 connector pin numbers
given by Audi in this schematic are the left-to-right reverse of those used

in standard telephony practice.)

Keep in mind that each kit for each phone is slightly different, each being

wired differently. You must, therefore, go through the entire design
exercise for every kit type being interfaced (even the "same" kits undergo
design/wiring changes over time and must be re-evaluated at every
occurance). The directions below are as specific as I can get.

This being said, here's how to do it:
- Buy a handsfree kit, for your phone, that has an external speaker and
  microphone (this type of handsfree kit already has all the driver
  circuitry you need). Throw the speaker away. Save the microphone, as
  you may need it later.

- The leads from your handsfree kit cradle now need to be connected to
  the proper pins on the DB25F in the trunk.  If there are less than
  eight wires needed by your kit, they can be routed to the trunk via
  the installed handset connector and wiring. If there are more than
  eight wires, you will have to route them yourself.

- If using the handset wiring, fabricate a DB25M that loops the signals
  from their source/destination pins to the proper pins (selected by
  your own cradle-to-car wiring scheme) of the RJ45. Put an 8-pin RJ45
  on the end of your cradle wiring to allow it to plug into the console.

- If running the wires yourself, make a harness, with a DB25M connector
  at the end, that connects your cradle's wires to the proper pins on
  the DB25F carphone connector in the trunk.

- Mount the phone cradle, plug everything in, and you're done!


Notes:
- Make sure to observe proper electrical practices (fusing, wire gauges,
  etc.).

- We have experienced impedance matching problems between some handsfree
  kits and the Audi microphone.  In these cases you will need to use the
  microphone that came with your kit.

The process is simple for someone with an electronics background. However,
IF NONE OF THE ABOVE INFORMATION IS CLEAR, QUESTION WHETHER OR NOT YOU WANT

TO ATTEMPT TO DO THIS ON A $25K-PLUS CAR.

Good luck!