Where is the manuel transmission fill hole for a 1999 cougar?

I just did this about a month ago. Jack up the front end, just enough to comfortably reach under the front end to the transmission. Also it will move the fluid to the back, which might be a good thing if you are filling it.

The fill hole is located on the front of the lower transmission housing. You should see a bolt or an inverse square-drive plug. Remove this and use a fluid transfer pump to add or remove fluid as necessary