Ford Explorer Sport Trac Owner's Manual page 211

Attach LATCH lower attachments of the child seat only to the
anchors shown.
If you install a child seat with rigid LATCH attachments, do not tighten
the tether strap enough to lift the child seat off the vehicle seat cushion
when the child is seated in it. Keep the tether strap just snug without
lifting the front of the child seat. Keeping the child seat just touching the
vehicle seat gives the best protection in a severe crash.
Each time you use the safety seat, check that the seat is properly
attached to the lower anchors and tether anchor. Try to move the child
seat from side to side. Also try to tug the seat forward. Check to see if
the anchors hold the seat in place.
If the safety seat is not anchored properly, the risk of a child
being injured in a crash greatly increases.
2008 07+ Explorer Sport Trac (esp)
Owners Guide (post-2002-fmt)
USA (fus)
Seating and Safety Restraints
211