Ford Mustang Owner's Manual page 146

8. Double check that the retractor is in the
automatic locking mode. Try to pull more
belt out of the retractor. If you cannot, the
belt is in the automatic locking mode. See
Figure 8.
Checking the retractor
9. Check to make sure that the child seat is
properly secured prior to each use. If the
retractor is not locked, repeat steps 4
through 7.
To remove the retractor from automatic lock
mode, allow webbing to retract fully to its
stowed position and the retractor will
automatically switch back to the vehicle sensitive
locking mode for normal adult usage.
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