1994 Lexus ES300 Factory Amp Wiring

I do not have that info and bet it will be difficult for you to find it anywhere.  I'd recommend trying a speaker popper (9v battery with wires attached to each terminal).  unplug the harnesses from the amp, and test for voltage using a multimeter. test with the head unit on and with it off, to find the amp turn-on wire, as well as the signal input wires for the amp (they will have varying voltage readings but should all be at least 1v).  The remaining wires are going to be your speaker wires.

With the speaker popper, try pairs of those remaining wires until you hear one of them make a popping noise.  Once you find a match, then plug it back into the amp, turn the system on, and test for voltage across the pair of wires.  positive voltage means the positive battery terminal of the speaker popper was connected to the positive speaker wire.  negative voltage means the negative battery terminal of the speaker popper was connected to the positive speaker wire.

Just continue until you find the remaining speaker wire pairs.