Please see the photo below. I have put white boxes in the photo around the two components that I've wondered about for a while now. Both are located under the airbox of my 97 XJR.

One clearly has something to do with vacuum and I suspect may be associated with the cruise control.

Also, note the smaller box around the white nipple. This nipple has a hole in the end, but no hose or cap covering it. I wanted to verify if it is correct with no hose or cap and open to atmosphere.

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Yes you are correct Al, parts of the cruise control.
Have attached PDF showing details.

John Herbert
(1996 Jaguar XJR)

 

The larger box is a vacuum pump, the smaller box is the dump valve.