I have had the nightmare of replacing speed sensors on a 1993 Ford Taurus and a 1997 Ford Taurus. The 1993 had 128000 miles and the 1997 had 70000 miles. Having been a back yard mechanic for many years and rebuilding antique cars it was very frustrating to see this type of system created for a car. The interesting thing was that the shop I took the 1997 to stated that the car will go into "limp mode" when the sensor goes bad. I am just waiting for the first law suit against Ford for someone hurt when they are not able to drive from a dangerous situation because of a sensor in "limp mode".
In addition to the 1997 sensor failing, I was selling it to a woman who said her brother designed the car. Think of the fun conversation I had with the woman when I had to explain that her brother designed a peice of crap...

Enough of my rant. This forum has been very helpful so I will pass on my knowledge. The 1993 speed sensor is located on the top of the transmission. The way I got to it was to put a towel and blanket on top of the engine a lay on the engine/cold with my head towards the windshield so that I could reach in back of the engine. After bending couple of clips out of the way you can reach the sensor bolt with a 10mm socket and short extension. unbolt it and the speed cable from the engine block. Carefully pull the sensor/unplug and unclip-I suggest you pick up the part first so you can see the connections-I paid $18-. Carefully put the sensor back in-I suggest you use disposable gloves and change them so that when you handle the new sensor you do not get dirt/oil on the sensor-also you will need to re-use the gear off the old sensor on the new one-remove the clip and re-attach to new sensor.

On the 1997 I remember the sensor to be located towards the rear of the engine compartment on the passenger side as you face the front of the car.