From what I can read via the STAR DVD for the R-Class, the disc changer retrofit is plug and play. You have to remove the radio and install a new wiring harnes (MB calls it a MOST fiber optic cable), you have to remove the old harness, install the new one and this new one connects to the harness on the CD changer. Do some work in the glove box to mount the changes, pinvolves removing the plastic tray (top left of glove box). punching out a plastic cover in order to install the button you push to drop down the disc changer, route the wiring harness and plug it in, put everything back and you will have to have the dealer configure the new MOST harness via STAR DIAGNOSIS software. The complete instructions for this are on the MB STAR DVD, I suggest getting the service dvd from MB (search the r-class forums for the info on this) and follow the instructions, they contain some pics and fairly good instructions. Good luck.