I'm also doing a search here and online, but I wanted to check the resources here too.

Does anyone have a simple schematic/wiring diagram on hand for the audio system in my vehicle? I am looking at the one in the service manual but since that doesn't help me, I'm not sure what I would learn from a different one....

I noticed that the rear door speakers are quite faint. When I adjust the fader to the front, they turn off completely. When I fade to the rear, they don't go any louder (let's say they're at 1 out of 10 at most.)

What I'd like to determine is what feeds these speakers so I know what wires to start looking at first. Since both are acting the same, I'm guessing its an amplifier issue.

Recently I had my subwoofer disconnected while re-foaming the cone and listened to the radio while it was out and I hope I did not damage the amplifier by doing that, however the sub and other speakers still work so...

Just trying to figure it all out.

if you have a new aftermarket radio installed, i would put a good nice 6 or 8 channel in there, the class d amps are small, but it will cause some radio interference.

if you can take out each speaker to test, making sure the speakers are good, then the amp is the problem. remember under the front seats have enough space to put a decent size amp.
i run multiple amps since i can upgrade the power later on.
also if you used those amp integration, make sure the wires are not pinched or grounded by accident.