2002 tahoe stereo install question

hooked up a pioneer deh-7500mp head unit in my 2002 tahoe (sub w/ onstar). Everything works but I get no sound (so I guess not EVERYTHING works). Came to learn later of the amp behind the glove box. Do I need something special to power the amp with my pioneer deck (additional wiring harness, etc.)? I figured as long as I had the remote power wires hooked up all would be fine. This is the first time I've had to deal with the factory amp. Any suggestions/help would be greatly appreciated.

I have yet to install in an 02 Tahoe, but I do know that in most of the Ford vehicles with factory amps, there is a blue/white wire on the Metra wiring harnesses, which must be connected to the CD players amp turn on lead. I am not sure if the harness for the 02 Tahoe has this, but something to look into. Otherwise, you probably need some sort of interface with the OnStar system. I am just trying to use my previous installation knowledge. Good luck.

correction. it was a blue wire on the metra harness.

hey try this....look at the harness(the factory harness) and see if there is a wire that goes into the factory harness, but does not have a wire on the other side of it...which would be coming out of the metra harness.  if you find one, cut it in front of the factory harness(leave about an inch of wire on the harness though in case it isnt the right wire, so you can connect it back together)and run it to the amp turnon wire from the head unit.  that should work, ive done it before.  its a possibility that the metra harness just doesnt have a turn on lead for the factory amp in your truck.

I kind of figured it out on my own. There is a 2nd harness plugged into the factory deck that runs to the remote tape deck. I figured that there had to be a remote power wire in that harness. So I found that wire (it's pink in that 2nd harness). I cut the remote lead off the metra harness and wired it to that pink wire and everythings works great!!! Now, if the kid at Best Buy had only given me the right mounting kit I'd had that thing installed by now. Guess that's tomorrow's project. Thanks everyone for your help.  Also, for what it's worth. My door chimes still work after removing the factory head unit. It sounds like there's some debate on that. Thanks again.