From a search of the archives I came across this:
With the C, you don't need anything but the unit and remote. It installs in about 30 minutes in the trunk under the black cover in front of where the spare is. All of the needed wires are there. I have done a dozen or so and they are easy.
This is what you said about adding keyless entry to a C class. I have a 96 c220 that doesnt have the keyless, so can u please elaborate as to what is necessary? Are you reffering to an original MB part? Or will any keyless entry system integrate. I am definintely interested in adding keyless, and this seems like the best solution.
Thank You for your time
Best wishes and take care,