Ford 2012 Mustang Owner's Manual page 217

If you cannot move the gearshift lever out of P (Park) with ignition in
the on position and the brake pedal pressed:
1. Apply the parking brake.
2. Using a flat head screwdriver or
similar tool, remove the cap.
3. Locate the access hole at the
front of the area under the cover.
4. Insert the screwdriver or similar
tool into the hole and press and
hold the lever forward while pulling
the gearshift lever out of the P
(Park) position and into the N
(Neutral) position.
5. Reinstall the cap.
6. Start the vehicle.
If it is necessary to use the above procedure to move the gearshift lever,
it is possible that a fuse has blown or the vehicle's brake lamps are not
operating properly. Refer to Fuses and relays in the Roadside
Emergencies chapter.
WARNING: Do not drive your vehicle until you verify that the
brakelamps are working.
WARNING: Always set the parking brake fully and make sure
the gearshift is latched in P (Park). Turn the ignition to the off
position and remove the key whenever you leave your vehicle.
WARNING: If the parking brake is fully released, but the brake
warning lamp remains illuminated, the brakes may not be
working properly. Contact your authorized dealer as soon as possible to
have the system serviced immediately.
2012 05+ Mustang (197)
Owners Guide, 1st Printing
USA (fus)
Driving
217