I put a new sub in my 04 and got nothing when I turned it on. Took it apart and put it back together twice before it occurred to me it might be a fuse. I think it may have been a 20 amp, but whoever had it before me had removed the fuse completely to disable the sub, so it was just an empty slot. Popped on a fuse and voila, problem solved. All the other speakers don't run through the factory amp, because my system sounded fine without the sub, it's just much better with it!