Ford stopped making the Thunderbird in 1997 and didn't start again until after 2000. So you don't have a 1998 Thunderbird.
If there is no brake lights on a 1998 Mazda pickup, check the fuse. If the fuse has blown, the lights will not work.
There is a shifter interlock switch on the brake pedal which also controls the brake lights
try the brake switch on the back of the brake pedal
What fuse controls the brake lights on a 1998 Chevy Camaro? It should be labeled on the fuse block.
Where's the fuse situated for brake lights on a Peugeot partner 1998
Blown fuse or defective brake light switch.
Bad brake light switch
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check fuses & brake lights switch located on brake pedal
Brake switch needs replaced.
It is important to pay attention to the warning lights on the dashboard. When the ABS and brake lights flask that means there is something wrong with the brake system.
Adjust or replace the brake light switch.