Ford 2005 05+ Mustang Owner's Manual page 158

If you cannot move the gearshift lever out of P (Park) with ignition in
the ON position and the brake pedal depressed:
1. Apply the parking brake, turn ignition key to LOCK, then remove the
key.
2. Using a flat head screwdriver, remove the plastic cover.
3. Insert the ignition key and push it
straight down to release the
interlock.
4. Apply the parking brake, then shift to N (Neutral).
5. 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 brakelamps are not
operating properly. Refer to Fuses and relays in the Roadside
Emergencies chapter.
Do not drive your vehicle until you verify that the brakelamps
are working.
Always set the parking brake fully and make sure the gearshift is
latched in P (Park). Turn the ignition to the LOCK position and
remove the key whenever you leave your vehicle.
If the parking brake is fully released, but the brake warning lamp
remains illuminated, the brakes may not be working properly.
See your authorized dealer.
2005 05+ Mustang (197)
Owners Guide (post-2002-fmt)
USA (fus)
Driving
157