There are 2 sensors, and 1 module.
The sensors are just behind the bumper, just above each frame rail as it comes forward fo the radiator support.
On my `97, the module is in the far right hand corner of the firewall, below the A/C & Heater Box. It's a BLUE box about 5" x 6", with 2 plugs coming in from the bottom. There are 2 screws holding it to the firewall, and 2 more screws holding it to the side.
I was told that they started putting side impact sensors in the Explorers sometime around the switch to the `98 body...
Ryan