W140 Head unit replacement

Hi everyone.

Did a search on the subject, some of my questions were answered, but some still remain... Steve, of course, is awesome with his responses.

I have a 93 500SEL with original sound system (including 10 disc changer in the trunk). It seems ok, but I noticed that the balance may be a bit off (I had to shift it to R 3 notches to make it sound right to me), and head unit is a bit outdated already.... No search function, etc. I have a Pioneer DEH 4200 which I would like to drop in there. What problems am I looking at in terms of hook up and hardware installation?
Thanks in advance.

[Peter Guenther]

It is probably possible, you must be aware of some items that will have to be addressed.
You have the control unit in the dash (looks like radio w/cassette).
You have the tuner in the trunk (wich also handles the interface to the CD player)
You have the BOSE amp that all this stuff talks to (which feeds seven speakers) two each in the front doors, one each rear door, four in the rear deck, and one behind the rear view mirror.
If you feel you want to mess with all this stuff, plus the alarm circuit, and the muting relay since the car was cabled for a cell phone, go for it.
There is a quck check, take out the fender liner on the driver side, after removing the CD you can reverse the right and left audio leads coming from the tuner to see if it changes your balance. Is the balance also affected when you play a CD or tape? it would narrow it down to the tuner/amp. If the audio is also distorted in one or more speakers it probably is the BOSE amp $600 rebuilt, very common failure. The amp sits over the rear wheel. I had both redone and am happy, check the Becker web page they offer exchange/rebuild service.