[wiswind]

I just looked the Speed Sensor up on the Rockauto website for your 2000 3.8L windstar.
It has a version for "with speedometer cable" and "without speedometer cable"
My '96 was different in that it had a Mechanical odometer and speedometer.
It sounds like your 2000 has a mechanical speedometer and a electronic odometer?
If that is the case, the speedometer gets the input through a speedometer cable that is connected to the Vehicle Speed Sensor......
The Odometer and the PCM (computer) get their input from the electronic output from the speed sensor.
There are 2 outputs......1 mechanical and 1 electronic.
When the one on my '96 windstar failed, the speedometer worked just fine.
However, my transmission was having issues with shifting because the PCM, which controls the transmission shifting, did not get the input from the speed sensor to know how fast the vehicle was moving.
There should be a "P" code stored if the VSS is not working.
This code may or may not light the CEL. (not all codes light the CEL).
This is a code that can be read with a generic OBDII code reader.

Now, for the problem of not being able to connect with the OBDII code reader, I am NOT familiar with how the VSS could cause this.
I would try going to your local AutoZone or other auto part store that offers a free reading of your OBDII codes.
Maybe it is some issue with just your code reader?.......doing this will find out.