[Cobalt Blue]

Series 1 AU Fairmont Ghia here.

I installed a 2018 Pioneer DAB+ head unit using the Aerpro primary harness, which meant only the front speakers worked. So, In order to get the rears working, I simply cut the wires at the smaller 16 pin C232 connector, as I figured I'd never be going back to the Ford head unit. I couldn't be bothered feeding new RCA cables and a 12v signal wire from the head unit to the rear amp.

I can verify that to get the rear speakers working from the rear, boot mounted OEM amplifier, green wire 8 at the C232 connector, will be your 12v signal. It's the thicker of the two green wires on the C232 connector. Blue (+) 13 and black (-) 14 will be your right or red RCA channel and thin green (+) 15 and black (-) 16 will be your left or white RCA channel.

Green wire 8 was connected to the blue & white wire coming out of the Pioneer head unit. I used the cheap green and black RCA male plugs with screw terminals, as seen on Ebay, to connect wires 13, 14, 15 and 16 to the female red and white RCA connectors on the back of the Pioneer head unit. Turned the power on and voila!