park/neutral safety switch

i have replaced the park/neutral safety switch on my 99 durango after it came up with the code for it being the reason my check engine light is on. i tested the three wires leading into the switch itself but the only one without power is the black and white one. the only thing i can speculate is that whatever this wire is connected to is faulty, or the wire has been severed some where. so my question really is where does this wire go, and what else would it be connected to? if i can figure that out maybe i can get my problem fixed, so i can get my truck smogged and registered. is there possibly a relay between the switch and the power source it comes from? any help would be extremely appreciated.<!-- google_ad_section_end -->