It is a 3 way vacuum junction, but would it go in the back? Looks more like an engine part. part # is 1170780145. Didnt know if maybe the mechanic replaced it and just tossed it in the back.

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1996 E300 D
1992 300D
1990 Ford E-350 7.3 Diesel AKA "the Deep Fryer"

This is a three way vaccum junction. It cost about $6 new. It could really go anywhere in you vac system. I would bet it is just a spare part.

Pooka