I got a new head unit (Boss BE7ACP), and wanted to keep utilizing the factory subwoofer and Amp.
I've installed head units/radios before, so the tricky thing for me was where to splice in the 12v to 5v stepdown, as I've never used one before. (which keeps the speakers from 'popping')

https://a.co/d/2eE8H82

The wire harness for my particular vehicle.
Also, I only used 2 of the 3 clips provided with the kit. One had only a 'power antenna' wire, which is not used for this vehicle.

Axxess Interface AFDI5V Ford 12V to 5V Step Down,BLACK
https://a.co/d/gIZydip

This is the step down that sends 5 volts to the Amp so it turns on. (5 volts is all that is required to do this, not 12v)

I hope this helps someone out there.