FORD 2008 Explorer Sport Trac v.1 - Manual (Page 201)

If needed, when installing some high back child restraints, the head
restraints of the second row seating positions can be removed. Insert a
thin pointed object, such as a paper clip or pushpin, into the hole of
each head restraint guide and while lifting up remove the head restraint.
Store the head restraint in a secure location in the vehicle. To re-install
the head restraint, line the posts up in the holes on the seat back with
the head restraint strap facing the outside of the vehicle and push down
until the head restraint locks into place. Lift gently to ensure it is locked
into place.
If the head restraint has been removed from a seating position to
accommodate a high back child restraint, the head restraint must
be re-installed prior to use of the seat by any other occupant in order
to reduce the risk of personal injury in the event of a collision.
2008 07+ Explorer Sport Trac (esp)
Owners Guide (post-2002-fmt)
USA (fus)
Seating and Safety Restraints
201