Your brown line IS the shutoff "circuit". It should hold a vacuum depending on the position of the key. I would start with that circuit and find if everything on the brown circuit is operating normally.
You can isolate the door circuit by disconnecting and PLUGGING the yellow base lines at the firewall. Golf tees work well. If after isolated, does the car shut off, if no then it is not the lock circuit. Then do the AC lines. Same proceedure. By isolating the two systems in the cabin you cut down on a lot of searching.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car