So I bought a 2017 FX4 Screw Lariat... 401a package. 7 speaker stereo, factory nav, without the sub 😒. Forgot to check but it does not have one. I found one on ebay and thought it was powered, but I guess it's not. What else to I need to get this sub working? I know about programming the computer, but in hardware terms... I know the amplifier... But what about wiring? Is there a harness? What does the sub plug into? I found the factory plug /harness by the C pillar and don't know where I'm supposed to plug that into... Any help out there for me?