Most Modern MB's Come prewired for their phone system from the factory.

The prewiring Includes an RJ45 Connector in the center console, as well as a Mini UHF connector for tying into the factory antenna.

Most of the prewiring is in the trunk. The pictures are from my 2000 c230k, but all MB systems should be the same. Before you connect anything thoroughly test using proper test equipment, etc... If you dont understand something, ask, or print this and take it to a pro.

The primary prewiring is in a DB25 connector on the drivers side of the trunk.

My objective in doing this was to run an unswitched +12v line to the center console, to charge my bluetooth headset when the car is parked (as I leave it synced when the car is in operation) However the prewiring is extremely versatile and can be used to integrate almost ANY aftermarket phone system into the car. As a matter of fact I am seriously considering the purchase of a bluetooth car kit, as a result of this discovery, thats why I label this phase 1.

Now in my w202 the DB25 connector was on the drivers side, underneath the bose amp. It was wrapped in grey styrofoam held together with the german fabric electrical tape. After a few hours testing with the meter and the scope, I mapped out all of the connections of the DB25 connector.

First thing to do is remove the driver side trunk carpet panel. On my car this was held in by 3 expanding plastic rivets, and two screws at the front where it meets the seat (this may be a function of fold down seats).

Here is a pic of where the DB25 connector was in my car.



Here is a pic of the RJ45 connector in the center console:



Now here is where the beauty of these two connectors and what you can do with them. This wiring is dedicated to the OEM phone system, and does not interface or cross with any other electronic systems (except for the stereo).

You can easily make whatever connections you want to the system using regularly available connectors, and leave the factory wiring completely intact.

A DB25 Male connector is available at Radio Shack, it is catalog number 276-1429. It costs 2.59, which is almost 10 times the price of a real electronics supplier, but if you are simply wiring a power outlet in the center console or something, its not worth ordering from a mail order house due to shipping.

The DB25 Male looks like this



Now here are the pin assignments which make all the interesting stuff possible.

DB25 Pin assigments.

Pin 1 is the upper right hand corner of the top row (the top row is the wider one with 13 pins).

From there pins 2 - 13 are in order each one to the left of pin #1

Pin 14 is the lower right hand corner, (rightmost on bottom row), and pins 15-25 are in order each one to the left of pin 14

Pin assignments:

1 - Pin # 7 of the RJ45 Connector in the Armrest
2- N/C
3. Chassis Ground
4. Unswitched + 12 Volts
5. Switched +12 Volts
6. Pin # 8 of the RJ45 Connector in the Armrest
7. N/C
8. Pin # 2 of the RJ45 Connector in the Armrest
9. N/C
10. Stereo Mute (connect to Chassis ground to mute stereo)
11. Pin #3 of the RJ45 Connector in the Armrest
12. Pin #4 of the RJ45 Connector in the Armrest
13. N/C
14. Microphone (-) *** see note
15. Microphone (+) *** see note
16. Unswitched +12v
17. Chassis ground
18. Pin #5 of the RJ45 Connector in the Armrest
19. Built in Speaker + ***(see notes at bottom)
20. Microphone Sheild (the built in MIC uses a shielded coax cable for noise rejection, and it is available at this pin)
21. N/C
22. N/C
23. Pin #1 of the RJ45 Connector in the Armrest
24. Pin #6 of the RJ45 Connector in the Armrest
25. Built in speaker - ****(see notes at bottom)

This is not a true direct connection to the speaker in cars with bose. It is run through the bose amplifier (the speaker is in the front passenger footwell) and requires a LINE LEVEL signal. In order for this speaker to be active, pin #10 must be at chassis ground, which mutes the stereo, and activates this amplifier channel. Your car kit Must have a radio mute output connected, and you have to use a line level converter, to lower the signal to the point of not overdriving the bose amp input. Another option would be pulling the footwell, and wiring to the speaker directly (disconnecting it from the bose amp).

In cars not equipped with bose, there are two speakers on the drivers side rear deck, and one on the passenger side. The inboard speaker on the drivers side labeled "high quality loudspeaker" is the speaker for the built in phone, and can accept an amplified output (such as those provided by most modern phone car kits) directly.

Microphone notes: The MB built in Mic seems to have some sort of preamp... As such it will probably overdrive the inputs on most car kits. More to follow on this as i research it further.
A quick and easy solution would be to cut out the factory MB mic and solder in the one from your car kit in its place.

As you can see, since you have all the pins of the RJ45 connector in the DB25 Connector, you can easily run power to that plug. Since there are 8 pins, you can mount the "brain" of any car kit in the lower center console, and run speaker +, -, mic +,-, Ground, Switched +12v, Constant +12v, and radio mute all to an RJ45 cable, and have a direct interface into the MB phone prewiring.

Any questions please feel free to e-mail me.

geoandroulakis@optonline.net

Take care,

George

__________________
George Androulakis

Former Mb's:

1990 500sl R129 - 76k Original Miles - New project - Follow the saga http://90r129.blogspot.com/
1990 190E 2.6 148k mi (sold)
1989 420 SEL 246k mi (sold)
1995 C220 175k mi (sold)
1992 190e 2.6 74k original miles (sold)
2000 c230 Kompressor 122k miles (RIP)
1996 C220 149k mi (sold)
2000 C230 Kompressor Sport 127k (sold)

Current Cars:

2009 Mercedes c300 4matic
2006 Mercedes s430
2005 Jaguar XJR
2003 Cadillac Escalade