my 2001 mustang is stuck in park?

See pages 113-114 in your Owners Guide :

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Brake-shift interlock

This vehicle is equipped with a brake-shift interlock

feature that prevents the gearshift lever from being

moved from P (Park) when the ignition is in the ON

position unless brake pedal is depressed.

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. Insert the key and turn it to OFF. Apply the brake

pedal and shift to N (Neutral).

3. 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

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I asnwered this question a few days ago look for it. It was a best answer. Basically first check the brake lights if they don't work the unlock system won't do its thing. The little relay right near the shifter moves a blocking object to allow you to move out of park. If that part is not working even tho the brake lights work I ALLWAYS rip the lock relay system out of the car and FORGETABOUTIT!