I installed a Pioneer 4200dvd with the Metra kit last night, everything seemed to go well. Once everything was finished, all hvac controls and head unit functions worked properly, except there is no sound, nor any hissing out of any of the speakers. I originally had the front speakers (bose stereo) wired into some RCA's for the pre outs as recommended here. I checked the head unit speaker wire outputs by testing them with a small bookshelf speaker, and it produced sound. I rewired the front stage back to the wiring harness and double checked the rear speaker wiring, but still nothing. I've checked fuses and there is also no obvious wiring damage. Nothing seems wrong or out of place on the Metra harness.

What could be the problem?

 

Sounds like you didnt connect the Bose amp turn-on lead? I installed my headunit before the Metra kit was developed, so I can't be sure of what all it entails. But just from installer experience.