Fuzao

I have just bought a 1993 SC400 and it has about a thousand problems, one of which being the speakers. All but the passenger side speakers make no noise (I think) [the speakers in the rear seem to be making some kind of vibration, however, I don't believe them to be making any sort of distinguishable noise]. I've read that the amp can go bad, however, the trunk doesn't seem wet. I will try to look at to take a look at it tomorrow but what other issues could cause it to do this? As far as I'm aware all of them went out at the same time. Could the wiring between the door panel and the main body be the issue? Anything else? Any help would be appreciated.

I have the Nakamichi sound system btw.