I am doing almost exact setup using LLJ customs diy harness, except I have 1 shallow 10” sub & 5 channel amp. You have it backwards, I made the same mistake and had to swap them all. The audio signal comes from the factory module and goes out to speakers in original wiring.
I have question too while I’m here once you got it wired right… Does your car sounds still work properly after hooking up (i.e. blinker signal, startup sounds, etc.)?
Earlier I had just the front left speaker hooked up and blinker sound worked, but now after everything hooked up I can’t figure out what happened and car sounds aren’t working. Could it be for some reason because I got power & ground for LC7i from amp instead of from harness yellow & black wire like you? Also why do you have 2 blue remote wires going into amp (eta: oh nvm the second wire is probably to turn on your sub amp)?
Also not sure how to mount sub. Thinking maybe drill through metal floor and bolt with l brackets. Not sure if that’s overkill though or if I need to hard mount to anything at all maybe just carpet.
btw, very professional install, looks great.
ETA: btw, fixed the car sound issues by installing AC-LGD 20. Only need it on front speaker signal to LC7i.