G20 Stereo system ipgrade problems...whats with all the damn harnesses?!?

Ok folks...Ive been installing and designing audio visual systems for a while now and this is the first Infiniti that ive worked on. I bought the harnesses from Best Buy and there are two. However, when I pull out the factory radio there are three harnesses. 2 look like normal speaker wire connects/harness the other is a white small harness with smaller pins inside. What is the small harness for?? I hooked up the two harnesses that made sense (the regular looking ones) and nothing happens (no power to the new cd receiver). NOW...I took the factory cd player and hooked up the two regular looking harnesses and no power was supplied to that one. But when i hooked up the small pined harness to the back of the factory CD player there was power. What does this tell you? A wiring diagram would be GREAT! Thanks