According to the shop manual, there is a "back up light switch" located on the tranny. Unfortuneately, I don't know exactly where it's located or what it looks like (I haven't gotten there on mine yet).
There should be a neutral safety swith located on the trans or in depending on whether you have a c4, c6 or fmx. the Fmx is located at the shifter. The c4 and some c6s are located on the side of the transmission behind the kick down lever. It will be a half round disk with one or two wires running from it.