I have a 1998 Nissan Sentra that had the same problem. I bought a new brake light switch. It is located behind the brake pedal. I replaced it and still had the same problem, what the problem was that on the brake pedal bar itself there is a hard rubber contact which the light switch comes in contact and shuts off the brake lights, if the rubber contact breaks off. It will leave an empty hole where the light switch cannot make contact to shut off the brake lights. I replaced the rubber contact with a small flat screw and nut, now it works great.