Threaded hole top rear of block behind intake

[Highmilers]

Got a quick question- What is the hole that is on the top side of the block just behind the intake? Our old block did not have it drilled, and the newer block has a tapped hole that is almost (but not) a 1/4" pipe tap thread, maybe a straight thread. I figure that I'd better cap it if it's oil or water.
What is it, and what size is it? It would save me some time if someone knows.
Thanks!

 

[Rick 91GT]

There is one hole back there with threads that is blind, it does nothing but collect dirt.

Rear passengerside...

 

[Highmilers]

hole question

You're right. With the light I had, it looked like a port in the bottom of the hole, so I figured that it was oil or water. There is no porrt; it's just a blind bolt hole for something like a trans dipstick tube bracket.
Thanks. I'll let it fill with dirt.

 

[1993_GT]

Got a quick question- What is the hole that is on the top side of the block just behind the intake? Our old block did not have it drilled, and the newer block has a tapped hole that is almost (but not) a 1/4" pipe tap thread, maybe a straight thread. I figure that I'd better cap it if it's oil or water.
What is it, and what size is it? It would save me some time if someone knows.
Thanks!

That is threaded for the grounding strap on 90-93 model Mustangs

 

[dastang2]

that is for a knock sensor that the truck motors used.