I gotta brake light problem on a 99 nissan sentra they wont turn off no matter what. well unless i disconect the battery. so what would that be ?

If they won't turn off, then more likely it's the rubber pad on the backside of the brake pedal that failed. When this happens, the pedal arm is no longer thick enough to reach the limit switch. You can verify by looking up along the brake pedal arm - you should be able to see two switches, one of which the pedal doesn't meet when NOT depressed. If you push in the switch and the brake lights go out, then you a) have the right switch and b) need to replace the (inexpensive) pad that mounts to the pedal arm. [Yes, I realize this question is six months old; just thought since it's been viewed so many times, someone should address it for future reference]

Replace brake light switch