2002 Solara... it's actually a lot simpler than it looks.
If you had the JBL system, there is a wire that goes from the stereo to a plug on the right side of the gutted-out stereo area, which runs down to the amplifier and back up to the stereo area, and finally into the speakers.
The standard Toyota harness works fine from the stereo to the speaker wires...
http://www.crutchfield.com/S-Js52Vbvmy1 ... =120701761
You can find one for less, I'm sure, somewhere like Wal-Mart. The Toyota/Geo (1987-up) harness works fine; I took the one from my 1991 Camry and hooked it to my 2002 Solara with no difficulties (it helped that both stereos were Alpine units).