Anybody know what this hole is used for??? It is a threaded nut that is open into the wiper channel behind the firewall. The hole doesn't align with any spot in the AC box. I assume it is not used but will need a screw otherwise water can get from the wiper channel into the AC box.

 

Could be for the heater box. It's been a while but didn't think any of those went into the cowl vent area.
if you need to plug it, do it.

 

I am wondering if that is needed for the non-ac car or maybe in the early years of the thirdgen but never got removed later. It definitely goes through into the vent channel below the wipers. It had factory seam sealer over it on the vent channel side but no bolt that I remember. I have seen it in pictures of other cars but those don't show anything using it. I have cleaned out the seam in the channel and put in all new seam sealer in there so will put in a "filler" bolt and coat the vent channel side with more seam sealer.

 

It's Used For The Non AC Box