Help with 1990 Ford F-150 vacuum issues

[Snattlerake]

I think this is correct. I started to but there were cables attached that I wasn’t sure how to disconnect so I let it be for now just to not make a new problem.

Gavula Bothers garage on 1oth street. These guys are my goto troubleshooters.. They are in my opinion the best repair garage in OKC.

 

[MacFromOK]

The dash selector switch is probably the culprit.

That would be my guess as well.

Had an '81 Fairmont that the control assembly cracked open on. Took it out and wired everything back together with 'lectric fence wire. Worked perfect for all the years we owned it afterward.