Not sure what is what in the diagram since it's kind of small to read on my computer. There is a vent that terminates in the passenger compartment. 125 could be the part I was referring to, although I'm under the impression the switchover valve is the valve to the right of the brake booster.
It's too dark for me to see anything on my car now.

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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