My '90 300D has the usual MB automatic door thing and an alarm made by Excaliber. To deactivate it, I turn on the ignition, then throw a tiny switch located way under the dash. This makes the alarm stop beeping and the doors no longer close after 30 seconds delay.

Hope that helps.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)