Adding sub with stock radio

[xoBtihS yM]

Im having trouble figuring out which wires to tap into for a line out converter. Nothing is labeled in the rear doors and they're all the same color. 2015 golf. Id prefer to just splice the wires in the b pillar (first photo) instead of killing myself to get wires through from the door.

 

[c31561]

These should help. Wiring diagrams for the left and right door speakers.