That is not what most of you think it is...MUST HAVE A TANNED NECK!!!
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While the switch is Poorly McGivered. It is not for applying brake lights.
It is a cut off switch apparently this guy could not remember which way was on so made a sign he could see even at night.
All law enforcement cars had them before about 1990. After that only certain cars have them. The printing on the switch is so small you can never read it.