where to grab source for aftermarket subwoofer

[135Hoser]

Hey,

I was checking on shopkeypro/identifix, and I can't seem to find wiring diagrams for the 2012 bmw m5's audio harness.

I know a adapter exists that takes the signal from the head unit before the amp, but I'm only looking to tap into the rears/existing subs.

Should I just grab my signal right from the under seat subwoofers? Does anyone know which pins these are?

Also does anyone know what pin I can use in the trunk as the remote wire?