Ford 2003 Mustang Owner's Manual page 82

Seating and safety restraints
Allow the belt to retract. As the belt retracts, you
will hear a clicking sound. This indicates the
safety belt is now in the automatic locking mode.
How to disengage the automatic locking mode
Disconnect the combination lap/shoulder belt and
allow it to retract completely to disengage the
automatic locking mode and activate the vehicle
sensitive (emergency) locking mode.
After any vehicle collision, the seat belt
system at all outboard seating positions
(except driver, which has no "automatic locking
retractor" feature) must be checked by a qualified
technician to verify that the "automatic locking
retractor" feature for child seats is still functioning
properly, in addition to other checks for proper
seat belt system function.
BELT AND RETRACTOR ASSEMBLY MUST
BE REPLACED if the seat belt assembly
"automatic locking retractor" feature or any other
seat belt function is not operating properly when
checked according to the procedures in Workshop
Manual.
Failure to replace the Belt and Retractor
assembly could increase the risk of injury in
collisions.
82