Stereo & Electronics - 93 Z/28 3 speaker Bose questions

I recently purchased my f-body for cheap. After fixing everything mechanical, I focused on replacing the crappy Jensen head the previous owner installed, or had installed. I have never seen such a rats nest of wires. Nothing labeled, Front, and rear channels hooked together, etc.

So basically, Ive got two quieries.
1. Can someone give me a rundown on the wire colors, and intended functions. Ive already established B+, switched, and ground, and of course, the antenna.
2. Are there wires run for rear seat speakers pre-exhisting, even though it was a 3 speaker system, or do I have to run new lines. Thanks.

Been a long time since I did my stereo in my 3 speaker Z28. I just ended up rewiring it, replaced head unit. Bypassed the Bose amps. There were no wires for rear speakers.

I have no issues with running new speaker wires. Im primarily looking for things like the dimmer etc.

Whats Id really like to do is run new wires for the 4 main speakers, and still use the factory amp to run the single speaker in the rear. Is this possible?