Ford THUNDERBIRD 2004 Owner's Manual page 115

When the key is in the ignition and in the OFF position, the
automatic transmission shift lever can be moved from the P
(Park) position without the brake pedal depressed. To avoid unwanted
vehicle movement, always set the parking brake.
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.
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 dealer or a qualified service technician.
Driving
115