Techworlock

I just purchased my 2004 4Runner and love it! I had to order the owners manual as it did not come with it and I have a question about the passenger audio system for the back seat.
In a nutshell I can't get the speakers in the back seat to work. I have tried the fader of course and I get nothing. I was wondering if it may have something to do with the passenger sound control, or if there is a fuse dedicated to the rear door speakers, or if I just need to take it in for service? I'm not real clear on how the passenger audio controls work; is the head unit duplexed or what? Any help would be greatly appreciated and repaid with a cold beer at my favorite bar if you're in the area!
Cheers!