Ok,

So what's the purpose of the Capped plug hole on the air filter cover? It taps into the clean air side of the filter intake. Is that a ford one size fits all air filter cover and not needed here or did ford connect a sensor to that port/plug/hole.

 

You're talking about the N/A filter housing lid? Never seen it hooked to anything. I personally used it for a project or two but stock it's unused AFAIK.

 

I believe it's for mounting a restriction gauge on the International version.

 

Yes, NA. That all makes sense. I just couldn't find any reference anywhere on this. So this could theoretically be used to create an indicator light with a pressure difference/vaccum sensor or gauge to inform you when your air filter is clogging up.

 

Yup! In fact I did just that. I think it was cheaper to buy the type that pressed into a grommet so I did that instead of using the port though.

And that's what Ford Six said with "restriction gauge"