There are five of them in a row mounted behind the pushbutton unit. There are two vacuum lines and one wire (?) going to each one. They can be tested by putting 12 volts to them and seeing if they open and close so that vacuum can flow thru them.

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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