its easy to replace if you can get to it, all it takes is like 2 bolts. It will be the sensor above where the drain for the mtx75 transaxle. I dont know about the Automatic but I assume it is the same. I had to take mine off to pull the tranny, just unscrew and pull out. I have no idea about the part number though.
I have a 2001 zx3 focus MANUAL TRANSMISSION. That's what I selected for vehicle speed sensor from the website provided, and I certainly did not get the right part. It wasn't even close. I took the part number off of the original one that I took out, so I'll be going to the stealership tomorrow to probably pay twice as much.