External Amp Location/Aftermarket Deck Problem

I have a 2002 XG350 and I am replacing the factory cd player with an aftermarket pioneer headunit.  Problem is when the harnesses are connected either there is no sound but everything else works on the aftermarket headunit or if i connect the remote from the aftermarket harness to the factory harness the speakers work but at an excessive volume and it overloads the circuit popping the fuse for the passenger side parking lights but the deck will still function after the fuse blows(2 fuses 1 circuit).  I was told my xg has a factory amp I need to bypass so any suggestions on where the factory amp is located or bypassing it without running all new wires would be excellent.  Also any mods know for the xg's and where to find them too.  Thanks

can't remember off hand where the amp is located but you can try looking in either sides of the rear quarter panels.  

Unless i am completely wrong, I think each speaker has its own amp. I put some subs in my car and in the back I saw that each speaker has a box with wire that was hot when the car was on only going into it. I don't know if that helps you or not, but its something I noticed.
good luck.