It's hard to believe that MB produced one of those howling idiot alarms back in '83. And dealerships like to add alot of aftermarket junk to vehicles to pump up their profit margin. Do you know where the car was originally purchased?

Otherwise car audio shops generally double as alarm installers. I will betcha they can indentify the system and even custom tailor it to your specs, say keepin the ignition cut-off but losing the siren. Or else neighbors will start hurling eggs at your car and who can blame em?