The following are steps it took to install Ipod aux input on factory Becker 3309 Mercedes head unit (used 1999 - 2002 model year) for free. I believe this is called a tape deck hack since a blank tape has to be put in for the input to work. This method will give you crystal clear digital sound WITHOUT FM modulator interference and you get to keep stock look that no one wants to steal. Also, steering wheel volume controls remain as well as the obsolete CD changer.
**Please proceed at your own risk and make sure you have an extra head unit handy if you don't know what you are doing.
If you are familar with mercedes radios, this can be done in less than 20 mins from start to finish.
This head unit actually came out of a 2000 w208 and it is the same as the one in the w210. I also did a hack on my 1998 E320 but it was much easier to figure out since the technology wasn't as small (1996 - 1998 used different head unit) plus it was marked "L" and "R" right on top of the tape unit circuit board.
1) pry off top of unit.
2) remove all screws from bottom of the unit. I believe the thick aluminum amp heat sink/cooler can remain on the back.
3) remove two screws from that attach the face plate then gently pry lever to tape deck door to left as show until it snaps off the brass peg. Look very closely on how the spring is set on the lever and how the lever goes thru the front before removing it. The spring might have to be set back in place. Once off brass peg unsnap clips to release faceplate forward.
4) Now you are ready to remove main board from the base so you can get to the botton to begin soldering. Three solder connections are required A) red (right) B)white (left) and C)ground wire (exposed or black depending on your cable)to ground point.
Solder the wires to the two points shown on the board. (ignore the black marker marks, i put those there for my reference). The right and left channels are almost side by side. Next solder the ground wire to the radio chassis or under a screw. Make sure the ground wire is insulated/coverd so it does not touch and short out anything on the board.
5) Blank cassette tape with all its guts removed must be used. If not the ipod plug interface in mentioned in post4 below will get warm. See last picture in series of the gutted cassette tape that is required.
6) Enjoy crystal clear music. I have done this to two of my mercedes that still have factory radios and now I almost never listen to my FM radio.
Link with info BECKER 3309-Mercedes Benz MY98
Please see YOU TUBE DEMO link below:
Let me know if it was easy and worked well for you.