reverse lights

i have a 2004 mazda 6 5 speed manual...when i put it in reverse the lights dont go on...ive brought it to NUMEROUS places and they said that it was a switch in the transmission...i talked to a friend that i work with and he said that i could take out the center console and look at the wires there and figure out if i have loosened one or sumthing...i just recently installed a custom stereo and took apart the center console and i think thats when i did sumthing to it...ne advise on how to fix it or a wiring diagram? plz help
 
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