Since the engine shuts off when you lock the drivers door, and since the drivers door lock doesn't control the other doors, I believe you need to look at the vacuum lock switch in the drivers door....take off the interior panel and plastic and check it out...you either have a vacuum fitting that has fallen off or is cracked (thats my guess), or you need a new switch...It is very obvious how this switch works when you see it.

Good luck

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)