my "stop light switch" has gone dead and needs replacement

I was told by ford dealer in my neighborhood that the problem I described to him was that my "stop light switch" has gone dead and needs replacement, and that this was common in the 2003 ford explorers. But he was not allowed to give me information as to where the stop light switch was located or how to replace it (go figure also they ,the dealer wanted $90.00, I ordered one from auto part store for $18.00!)Where is it located and how do I replace it..also any tips on how to bypass it in the meantime so I can move my vehicle. Any information would be greatly appreciated.