Vacuum Type Door Locks
Found mostly on Mercedes Benz vehicles, the movement of the door lock actuators is controlled by a central vacuum pump. The switch changes polarity on a single wire that may rest at power or ground depending on the state of the door locks. You can duplicate this with at least a 2 second pulse. If the alarm or keyless entry you are installing does not have a 2 second or longer duration option for the door lock outputs, do not use this diagram (it will not work unless you incorporate a timer into this circuit).





This info and diagram was obtained from : http://www.the12volt.com/doorlocks/page3.asp#vac

I am not connected or affiliated with that site, they just have some great info on the site. I used this setup on my 190 and have not had any problems. However, I do recommend that you test all connections and fully understand what you are doing before cutting into the factory wiring. I tapped into the factory wire under the drivers side floor mat in the wire channel next to the sill plate. I will dig up the wire color codes tonight. Good luck