07 lexus ls 460 stereo

Im installing a system in a 07 lexus ls 460 and the customer wants to keep the factory head unit since it is touch screen. Can anybody tell me wherr the factory amp is and what color wires i need to tap into wit the moduleNick Miller

     Battery BLUE (+) RADIO HARNESS      Accessory LIGHT GREEN (+) RADIO HARNESS      Ground WHITE/ BLACK (-) RADIO HARNESS      Illumination GREEN (+) RADIO HARNESS      Power Antenna BLACK (+) RADIO HARNESS      LF Speaker (+) RED      LF Speaker (-) BLACK      RF Speaker (+) WHITE      RF Speaker (-) GREEN      Amp Location BEHIND TRIM IN RIGHT SIDE OF TRUNK

Does anybody know what plug and what wired on the factory ampNick Miller