If you are running a factory head unit , and rear speakers a speaker impedance simulator will allow the fader to be correctly coded, without it the fader will not displayYeah there's a Y cable thing, I should've taken more photos.
Got it all from Sean at CEN I think (I have a cold and my mind is fuzzy) he also sold me a speaker impedance emulator thing, not sure that was necessary as I see other people fitting these and no sign of that part.