Where is the fuel cut off/inertia switch?

The usual location for Ford vehicles is behind the passenger side kick panel trim forward of the front passenger side door usually snaps off but there may be one or two small screws to remove .

Thanks Clif, That is where I looked and saw nothing that looked like the housing or red button. I have a box with several wires extending from the bottom. Passenger side, front seat, behind plastic side kick panel 1999 Explorer 4dr, XLS 4.0l engine

If you have the owner's manual it should show the location. If not, search the net and you can probably view one. The ford website may have an on line owners manual you can view.