I have a 2000 Explorer. I think it's the same as yours:
If you're sitting in the front passenger seat it is on the right kick
panel above your right foot. Check your owner's manual, it should be in
the roadside emergency section. In mine there is a drawing showing the
location. You may need a flashlight to see it.
-Paul

That's where it is. Make sure that the switch is reset and the connector on
the bottom of the switch is fully engaged.
It's possible to have the passenger kick the connector loose if they have
their feet up on the firewall in front of the passenger area. (experience
speaking here...)
Good luck,
Brian