Ford Mustang Owner's Manual page 142

4. Insert the belt tongue into the buckle for that
seating position until you hear and feel the
latch engage. See Figure 3. Make sure tongue
is latched securely to buckle by pulling on
tongue.
Buckling the belt
5. Grasp the shoulder portion of the belt and
pull downward until all of the belt is
extracted and a click is heard. At this time,
the retractor is in the automatic locking
mode (child seat restraint mode). See
Figure 4.
NOTE: The dual-locking mode retractor must
be in the automatic locking mode to
properly restrain a child.
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