i tapped behind the headunit
Not knowing what year or what grade of stereo the orginal poster has, behind the radio is a start.
I used to drive a company leased 2006 Ford Escape. I installed an amplified Bazooka tube with the intent of upgrading to a better subwoofer system later. The radio popped out via the removal tools you can buy anywhere. Not only did buy the aftermarket radio harness (plugs into factor harness and gives bare wire to connect an aftermarket radio), but I ordered the opposite harness (plugs in to factory radio and gives bare wire a.k.a. like you are repairing the factory harness). I made a "T" harness with my Line Out Converter and was simple to plug in. It gave me front and rear rcas. I installed a line driver to boost the line signal. But, I had to remove everything to turn in the vehicle.
Bazooka makes plug and play harness solution (never used it).
http://www.bazooka.com/products/mobile/ ... 7/FAST-S60
Even if you don't have a Bazooka tube, that harness and extension could be usefull.