No sound from Passenger 9' Bose, how to diagnose/replace?
 

So there's nothing coming out from the big speaker on the passenger door. Everything else works though.
Honestly I didn't even notice it till my girlfriend was sitting in the passenger seat.

When I was checking it, I found out that one of the wires on the passenger tweeter (aftermarket Infiniti Kappa) was loose.
When I reconnected it though, there's music coming through again. Could the loose tweeter have fucked up the big one due to the 1/2 ohm and all that? (Electronics noob)

Look up the thread on the Bose door amp repair. It's a common problem. If you tap on the door and the sound comes through for a moment, it's likely a bad relay in the amp.