OK, I gotta ask: unless you are planning on evading police, secretly stalking neighborhoods at night, or causing traffic accidents, why would you want to do this?
I would never do this of course, but ... I once knew someone liked to drive fast at night on lonely highways with extremely light traffic and no one in the lane behind him. During those circumstances ONLY, this person would, for brief periods of time, disable the brake light so that if he was hit by radar and had really fast reaction time, would not alert the radar operator that he was using a radar detector by lighting up his brake lights like a Christmas tree. If the radar operator sees a driver is slightly over the limit but does not overtly react to the radar targeting, they will frequently let the driver go. Conversely, if it is apparent to the radar operator that the driver is speeding and has a radar detector and is trying to evade detection, he is much more likely to pursue the driver. I realize this sounds hard to believe, but I have seen it work on more occasions than I can count. Basically, if the driver is very fast but also very smooth on the brakes and isn't going too far over the limit, he can get down to a speed that may be somewhat over the limit but is less than the radar operator deems to be worth pursuing.
Please do not flame me with 1) Admonishments that this is an unsafe practice and 2) No one has reaction times that fast: It does work on many, but not all radar encounters. It also is useful for non-radar encounters when trying to be somewhat inconspicous. For example a driver blows by a parked patrol car, and realizes it while going by. If the lights are off and the driver is smooth while braking, often the patrol car will elect not to pursue.
Obviously the use of something like this requires a driver to be hyper-disciplined in making certain to turn the switch back on when entering even light traffic. Otherwise a car approacing from the rear could get too close for comfort or worse. Ten years ago there was even a company that made a brake light kill switch that would kill the light for one brake application only, then automatically would reset to turn it back on. This would require constant hitting of the switch but it was a useful safety feature. Haven't seen this offered lately.
I'm not advocating that anyone do this, In fact PLEASE DON'T USE ONE.
I just thought I would respond to the question.