ive tried looking around a little bit and i cant find much on this issue. i looked at the thread about the 03's not working but it seems he has a lil bit different issue than im haveing. i bought the car with a factory head unit in it and i pulled it out to put my pioneer single din in and when i wired everything up the rear speakers wouldnt work. i checked the fade/balance on the pioneer and still nothing. i pulled everything back out and rewired everything and still nothing. the second time i pulled it out i noticed it already had a bunch of aftermarket eclipse wiring in there so im assuming there was previously a aftermarket unit in there at some point. so after all that i tried putting the factory head unit back in and they still didnt work. i dont think they ever worked, but i think i was never paying attention to if they worked with the stock or not. after all this i decided to pull the speaker covers off the rears and there are aftermarket infinity speakers in the rear. i was going to see if they were plugged in but i have no idea what all has to come out to see if theyre plugged in or not. has anyone else had this issue or know how it can be fixed? i know everyone says not to worry about it but im kinda ocd about lil **** like that and i like having all of my components working as advertised. on top of that, does anyone know how to pull the covers off of the rear speakers to see if theyre plugged in?

 

You'll need to pull the entire trim off behind the seats. Start by removing the glovebox, then remove the door sills and work your way back. You'll probably break a few clips if you don't know where to look (download the FSM if you haven't already and look at the clip locations). A clip puller comes in handy here. You'll need to remove the cubbies as well. Simply open the doors, reach in, stretch your hand and yank forward. Those come right out. The rear trim is quite large, and it helps if you have two people take it out. The speakers are exposed and come out with 4 screws. If you can't find where the wire was spliced, then run new speaker wire to your head unit.

 

http://liljerk.morpheus.net/350Z/rear_speakers/