To find it, you might need to:
* Remove the passenger-side kick panel: This is usually held in place with clips or screws.
* Feel around: The switch itself is usually a small, square or rectangular box with a button that can be pushed to reset it.
If you can't locate it easily, consult your owner's manual. A diagram might be included, or it may point you to a specific location. You can also search online for a 1991 Ford Explorer repair manual or parts diagram—many are available as PDFs.