suv wiring 1999 eddie bauer

Hi people!  I'm wondering if anyone's has any experience with these vehicles.  I am going to install a pioneer F90 Nav Head Unit for my Expedition.  The vehicle has a factory Mach Audio system in it.  A hidden Subwoofer.  Anyways, I want to install my two amps (4 channel for fronts/mono amp for subs), new head unit (F90), 2 subwoofers, focal speakers for the front and a monitor for the rear passengers.  Am I going to re-wire or bypass any of the factory wires in the vehicle?  Or can I just tap into the factory wires and wire up my speakers?  It has no Onstar (10 year old).  Will I need any interface products for this vehicle?  I once installed a head unit for a 2004 elcipse car.  I had to buy an interface to do it.  I also tackled a 2006 pontiac grand prix equiped with a monsoon system.  Big Mistake!  So if anyone has any heads up for me, It would be much appreciated.  Thanks.  My email is napew@shaw.ca 

Would you say I would have to lay my own wires to bypass the factory wires?

I think the factory amp is located in the right rear quarter panel.  Maybe directly behind the rear door.  You should be able to run your wires to that point and connect there.  I have no idea if they use standard Ford colors on the amp, but they should be pretty easy to figure out.  When you cut the wires from the factory harness, make sure you leave enough wire on the plug to be able to see the color of the wires.  Once you identify the speaker wires, it will help you determine positive and negative.

Thanks