I am reading this as you want to add a sub to your factory system that doesn't have a sub line, Right? I am also assuming you want to add a amp/sub/enclosure as your goal
If you DON'T have a factory system with the Sub just tap the rear Left and Right speaker signal. It should be full range and easy to get access to. Input those into a Audio Control LC2i to pull off the sub signal that can then be amplified. If you do have the sub line you can still use the LC2i in the same way to add bass control and boost features.
Maybe if you provided some more details on what you are starting with it might make it easier to help.
2500 Watts RMS!! Rockford Fosgate Amps (T600-4, T1000bd, P400-4), (2) 12" Rockford Fosgate P3 Subs in JL Basswedge Enclosure, Focal 3-way Performance P165V33 Component Speakers (Front), Focal Polyglass Series 4" Coaxial (Center), Focal Access CS-1 6 1/2" Coaxial Speakers (Rear), Audio Control LC8i processor, Custom Amp Rack and Cover with 24" x 14" Plexiglass Window, Lockpick V5 with Backup Camera
Last edited by SacTownMan; 02-19-2013 at 10:07 PM.