i have been chaging out all my vacuum lines slowly on my 1988 f150 5.0 and i cant find out where the top vacuum port on the vacuum tree on the intake manifold is supposed to go. when i got the truck it had an old plug on it with a hole in it and the guy before me put silicon on top of it to seal it.. didnt really work so i replaced it but is that supposed to be capped? or is it supposed to go somewhere

(new to working are cars trying to learn so anything is appreciated)

 

I have one of those caps on my 94.

There are 4 main small lines that run from the manifold tree. One runs to the fuel pressure regulator, one runs to the vacuum canister reserve, one runs to the map sensor, and one runs to the A/C system if you have it.

 

ohhhh alright that makes sence i dont have a/c or a heater�� it came that way

 

Caps are common