How do you adjust a parking brake that doesn't work on a 2003 Crown Victoria Police Interceptor?

the adjustment is made from under the driver side of the car, just in front of the rear wheel (it is a cable with a spring and a metal clip). Press and release the parking brake twice, then jack up the car (if you cannot get under it), using a flat screwdriver, pull the metal clip and the spring will pull the cable tight. Make sure the metal clip goes back (you may have to push it). If the spring is fully expanded then you no longer have adjustment and will probably need professional replacement of the parking brake cable or other parts.