Hey, maybe I'm missing something here, but aren't all you looking for is the line to your reverse lights? Doesn't the shifter you have contain built in nuetral and reverse light switches. If so, would you not be by passing the nuetral safety switch on your tranny and wiring them to your shifter instead? There should be a plug coming off of your nuetral safety switch on your tranny. That plug will contain the wires you are looking for. Carry out a continuity check to determine the correct wires for your shifter switch connections. Do you have the instructions for the shifter handy?

http://www.bmracing.com/bmracing/installation_instruction/7.pdf