Originally Posted by migs647

I wish I was there to help you. Something is off. We have the most basic set up in our cars compared to any other car I've worked on.

Did you have the antenna plugged in? There are some decks that will not ground properly without the antenna plugged in.

Is there a parking brake wire? At a minimum I'd ground it if there is.

Did you attempt multiple sources? (radio, iPhone, etc)

Our non sss speakers work fine with any deck. It would have been best to put a multimeter on one of the speaker lines (+ & -) and verify signal was coming out. If it wasn't, something is wrong with the deck. If it was, something was wrong with the harness / connection. Did you use butt connectors?

Originally Posted by W0LF

As previously tested, the issue is between the speakers and the headunit. I have already installed the new deck with the exact same harness (Alpine Uses the same harness between the 2 headunits). No issues other than the not so great sounding stock speakers at higher volume levels lol. I also soldered all connections and applied heat shrink tubing on all connections.

The only main difference I can see is that the deck that will not work has a 2 volt preamp output whereas the ones that are working have a 4 volt preamp output? I'm not very knowledgeable about audio equipment/wiring as I've always been a performance/mechanical kind of guy. Maybe someone who understands what this means could better explain.