I have a 07 GT with the shaker 500 system. I am about to install a new aftermarket head unit and I don't quite understand the wiring for the door subwoofers. According to the wiring diagrams only pins 1-4 are used in the shaker 500 system but the metra harness uses pin 4 for left (White) audio and pin 8 for right (red) audio. So when you plug the left (white) and right (red) plugs into the back of the head unit its only using the left channel for audio and splitting between both subwoofers? I attached a picture of the metra wiring harness and the factor pin diagram to better explain my curiosity.

 

Hi! Did you resolve your issue? Because I have same problem....

 

contact Crutchfield.com. They have a service where they will construct a wiring harness for your situation. They may also be able to help you without the need for a specific harness. Just a suggestion,