Where is the speed sensor on a auto 98 ranger 4-cylinder?

The speed sensor on a 1998 Ford Ranger 4-cylinder is located on the differential. More specifically, it's usually mounted on the passenger side of the differential housing. It's a small sensor with a single wire connected to it.

However, it's crucial to confirm this by checking your vehicle's repair manual or a reliable online parts diagram specific to your year and model (including transmission type). There's always a small chance of variation depending on specific options and manufacturing changes within a model year. A diagram will show you the exact location with certainty.