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.

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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,
George Androulakis

clarification of the info i need
 

Just to let u know, I am an experienced car audio / alarm installer. What I need to know is the location of the lock / unlock wires, as well as what polarity they need to perform their operations. In my 190E there was a blue wire that ran along the wire channel on the drivers side. You applied +12V to lock, -12V to unlock. It did require setting a longer pulse than came standard though, but that is no big deal.

The Vacuum lock system in my C class seems similar, except for the addition of the lock / unlock switch on the dash. And the disablement of the door lock buttons from operating the central locking.

Benzmac seemed to suggest that all the wiring is available somewhere under the plastic cover in front of the spare in the trunk. If anyone knows which harness these wires are in, and the color / location of these wires, it would be of a great help to me.

Thanks for your time
Best Wishes and take care,
George Androulakis

Hi,

I don't keep the wiring diagrams at home, but I will try to help.

There is a mat in the rear trunk, take it out. Under there toward the front of the car, there is a black cover with a few plastic nuts holding it down. Take it off and you will see a large bundle of wires and some room to install the controller. This is where all of the wiring can be done. You will have to get the colors, for I don't have them with me.

The pulses are negative to lock and unlock. Only on the earlier cars did you need the alternating polarity.