ok so i have been installing stereos for quite some time now and just installed one in my buddies 05 f150 lariat. i put in the new head unit. (pioneer avh4400bh) and replaced all of the door speakers and put them on a massive nx4 4 channel amp. i ran new speaker wire from the amp directly to each door for the speakers and it sounds amazing, but the factory sub doesnt work. ive never messed around w factory subs. i normally take them out and put big stuff in. im assuming its something to do with the fact that there were 3 wiring harnesses that came out of the factory radio and only one that wired the aftermarket one in. if anyone knows what i need to get or do to make the factory sub get signal/work again i would appreciate it

 

Yep, you are missing the adapter than takes factory sub out to rca. Metra makes the adapter.