Ford Thunderbird Owner's Manual page 135

7. Grasp belt close to child seat and pull on the
shoulder belt portion of the combination
lap/shoulder belt, then allow the belt to
retract and remove all slack to securely
tighten the child safety seat in the vehicle.
See Figure 5.
8. Before placing the child into the child seat,
forcibly tilt the child seat from side-to-side
and in forward directions to make sure that
the seat is held securely in place. See Figures
6 and 7. If the child seat moves excessively,
repeat steps 6 through 8, or properly install
the child seat in a different seating position.
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