Sounds like your ignition switch is ok, but I also am very confused.
How can your engine shut down (which you wrote that it did) if the fuel shut off valve is bad? And how can the engine shut down if you disconnected the line to the shut off valve, connected the Mity Vac to the line, but didn't T it back into the shut off valve?

I think what we have here is a failure to communicate.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13