1994 SC400 wiring nightmare

Okay, I just got this car, I was told by the seller that he bought it with no working stereo 5 years ago, and his wife drove it without one the whole time.  I had the dealership check out the head unit, and they said it doesn't work.  I don't know how they "checked it out".  THe seller also told me that there had been an aftermarket alarm installed prior to his owning it, and that the dealer who sold him the car had removed it.  I have found some pieces left over that would lead me to believe that part.  The head unit was not wired in nor does anything else seem to be as far as the stereo is concerned.  The A/C works but each time I start the car the A/C light starts blinking and it turns itself off.  I just have to push the A/C button to get the air back on, but this is my 7th Lexus, and I have never had any of them do that.  THe previous owner also told me that the amp was no longer in the car, I haven't gotten that far into the car yet but I am assuming if it is, it is blown.  Each speaker location has cuts, giving easy removal, so I think that there was an aftermarket stereo at some point also.  All the speakers (standard Pioneer) are in the car, but I don't know if any of them are any good.  I have the basic wiring info for the factory stereo and alarm, but I am not getting power to the factory system (head unit, CD changer).  The alarm pieces I have found are hooked into the stereo wiring but then go no where?

I know I have a lot of work on this one, and any suggestions are very much appreciated.  I want to just put a complete system in, only problem is I think the previous work done might have been just a bit creative.  Is there any where I can get more detailed wiring info?  I seem to have extra plugs, factory plugs that go to nothing, I even had a wire jammed in where a fuse should go!     Any suggestions, really!