stereo wiring 1995 lexus gs300

I am putting a stereo in a 1995 Lexus GS 300 and was unable to find a harness so I am having to wire it direct.  My issue is that all the speaker wires at the factory radio don't match with what it says on the website for these vehicles.  The power, acc, and ground all matched up fine.  I also think this car has an amplifier since it has a subwoofer in the center in the back under the rear window behind the rear seat.  When I went to looking for the factory speaker wires I found 4 gray sleeves with 3 wires in each one.  If anyone out there has ever dealt with this before or has a more informed view of how to wire this up to make it work please let me know as soon as you can.  ThanksDover

That car almost certainly has an OEM amplifier.  Your best bet is to replace all speakers and run an aftermarket amp rather than try to use the OEM amp and speakers.Support the12volt.com

I ran into this before on a 2001 chevy tahoe and it was as simple as just powering up the factory amp by connecting a wire to the factory turn on wire so that when the aftermarket stereo came on the amp did too.  Is it not possible to do this on this car?  I really don't want to replace all the speakers and buy an amp right now.Dover

This should help radio wiring diagram

So nobody makes an integration harness for this car?  And there are no other cars that share the same type of wiring or stereo system?Dover

I do not believe that there is a amp integration harness available for this vehicle. The diagram that I posted up should make it relatively painless to wire your system up.

Will I still be able to use the factory subwoofer or will it be inop?Dover

I do not see why not. Just make sure that you are not wiring the speaker outputs of your aftermarket radio into the OEM amp. I'm pretty sure those gray sleeves you mentioned in your OP are the low level inputs to the amp.

I have the diagram figured out but I am a little confused as to how I might go about utilizing the factory subwoofer without an amplifier.  I have installed alot of systems but this one is a little more detailed than I expected.  Could you give me some advice on getting the sub to work also.  Thanks, sorry if this seems dumb but i'm just not sure about the sub.  Thanks for all the info.Dover

I was under the impression that you are integrating the OEM amp into your design. If you're not, you're going to need to give us all the details you are planning.