The speed sensor on a 1998 Ford Windstar is located on the
differential. More specifically, it's usually on the
passenger side of the differential housing. However, it's important to note that its exact location might vary slightly depending on the specific transmission and axle configuration of your vehicle.
To be absolutely certain, you should consult a repair manual specific to your 1998 Ford Windstar. A Haynes or Chilton manual will have diagrams and detailed information. You can also find diagrams online, but be cautious and double-check with a reputable source before attempting any repairs.