Where is the 86 F-150 Vent air entrance?

[Gary Lewis]

Yes, you need a gasket there.  Do you have A/C?  If so there's a guy that makes those gaskets.

As for the plug, I can take a pic of Dad's truck today and probably show you where the plug goes.  But Dave already knows, so if I don't figure it out maybe he can take the pic?

However, I'm thinking you have a plug in that hole, it is just that someone at the factory dropped an extra plug in.

[Gary Lewis]

Here's what the openings in the cowl look like.  Your plug may fit the outer holes.  However, your plug appears to rectangular save for that one angle and the outside holes aren't.

So if it doesn't fit there then I don't think it is from your truck.  I've looked all of the other openings in Dad's cab and there's nothing shaped like that.  The only possibility is that maybe since Dad's is an '81 and yours is an '86 something changed?

[85lebaront2]

Right end in the picture of the bare top of Dad's truck cowl is a hole that shape. I knew I remembered seeing one that shape on Darth.

On the nut spinning, it probably stripped the T bolt when the trained monkeys on the assembly line tried to tighten it. I have some removed from old HVAC cases. Where was your truck built?

[Gary Lewis]

I'm not so sure, Bill.  The plug looks to have two right-angle corners and two 45's.  The hole on the right of the cowl doesn't seem to have any right-angle corners and the run across the bottom has a dog-leg in it.  

[Sac79]

The driver's side stays open, at least on mine, and is sealed in with the cowl cover.

[Sac79]

Gary, I think that plug just looks weird in the picture. I'm sure it's what we think it is. Mine was pretty crusty as well, but some warm soapy water does bring it back to some usefulness.

[archeman]

OK guys those pictures are perfect - much gratitude, that would have been hard to figure out any other way.
And yes it looks like I have found the home for my plug there.

This also helps explain why leaves were getting into my system so often and so fast.

I took a picture of the top of the plug, so it seems that at the factory the plug was installed from the top based on the shapes.  Re-installing it from the inside (upside down) might present an insurmountable challenge.

I'll have to consider my options.

[mat in tn]

Any chance you could try using a light and a mirror to see if a plug is installed? Bore camera or cell phone even.  As for the spinnin bolt. As was referenced before. Those studs are threaded on each end with a “t” in the center. The “t” fits into a slot n the plastic housing and a nut tightens it to the box FIRST then when inserted into the firewall the second nut pulls it tight against the gasket. If its spinning then the other end is loose and it is the fault.  Unfortunately the best way to correct this is with the passenger fender removed

[Gary Lewis]

Yes, I'd check to see if it is there.  I'm betting it is.  I wouldn't pull things apart to find out.

[archeman]

OK, I'll get a peek up see what is lurking there. Perhaps there still is a cap in place.
That may take a week or two.
The truck is 3rd in line at the moment behind my daughters Nissan cooling system and my son's Cadillac brakes.