You run both + & - speaker wires to the +/- on the RCA adapters. Some people cheat and use only one side since sub bass is mostly mono. My preference is to feed from both L and R sides and let the amp sum the signal. You can splice off and keep the rear speakers functional, but it were my car, I would unplug the rear speakers and plug these Metra 72-5602 speaker plug adapters so you don't have to molest a single OEM wire at all.Edit, so after looking, do I just splice one of or both rear speaker wires and then to those adapters?
never ran it like this, learn me