Brake light stays on - 1998 Nissan Frontier

Two reasons for the brake light to be on. 1) Parking brake and 2) problem with pressure in the brake lines.
If the parking brake is off and the ignition is on but the brake light stays on, then there's a problem with the switch attached to the parking brake. It might be stuck or broken.
If the brake light goes on when you apply the brakes, there is an imbalance somewhere in the brake lines between front and back wheels. This light usually goes out when your foot is off the brake, but if it stays on, the switch in the brake lines near the master cylinder might be stuck or broken.

Are you sure it is the tail lights and not the brake lights? If the park lights are staying on, the front should be on as well in most cases. If it is the brake lights staying on, suspect a faulty brake light switch located at the brake pedal

Do all brake lights stay on including high mount? If all stay on suspect problem with brake switch located at brake pedal. If just lower brake lights stay on ( not including high mount ) expect problem with multifunction switch ( signal switch )

be sure that brake pedal is all the way up even if you have to pull it up or thers a wire shorted

The regular brake warning light is for the parking brake being applied or the brake fluid is low. You would need to get the abs system scanned for trouble codes to proceed.

The warning light on the dash, or the brake lights in the back of the car ? ?
The brake fluid could be low or the parking brake switch could be faulty if the warning light is on.
The brake light switch on the pedal could be faulty if the brake lights are staying on.

If all the brake lights stay on then the brake light switch is the first thing to check. It cod also be dagger wiring to the switch or it may just be loose and/or out of place.

Check your brake switch as it could be faulty hence causing a close circuit which in turn causes the brake light to stay on.It is normally located at the top of the brake pedal.Hope this helps.

are you sure you the adjustment to it is correct the button in the end of the switch has to be fully depressed to deactivate the circuit