The transmission pan is located approximately in the middle of the car, there should be I believe 14 bolts, slowly loosen each bolt and let the fluid slowly drain as you may warp your pan, and your new gasket will not seal properly, "from experience"...lol. Make sure to tell the parts dealer if your car is equipped with O/D as your filter should have a plug/neck that is pressed into your tranny. The easiest way to check is to look under your car, and if your car is O/D then the tranny pan should be rectangular, and have a press imprint of the symbol Ford. Hope this helps a bit.
Inside the transmission
The answer is no. Not same engine either. 91 couger has a 5.0 (if its a v8) and a 3.8 (if its v6). a mark viii will only bolt up to a 4R70W transmission. A 91 couger does not come with a 4.6 ( The 4.6 Was not released until 1994)
It might be the transmission range selector
Replace the transmission computer. Located under the center console.
The transmission dip stick on a 1994 Mercury Sable is located on the driver's side of the motor. It has a white-handled ring and it is about midway between the radiator and the back fire wall.
transmission fluid is in the transmission
Dexron/mercon
on the steer wheel
1994 - 12.25 qts.See "Related Questions" below about transmission fluid capacity
Should be a plug at the side of the transmission- fill to this level
PCM, TCM, and internal transmission mechanicals.
It is in the transmission itself.