The colors are different on the 2002 harness. But there are 24 positions like your plug.
On the 2002
a1-empty
a2-empty
a3-power out to amp-orange
a4-empty
a5-empty
a6-empty
a7-empty
a8-lr speaker+ brown
a9-lr speaker- yellow
a10-rf speaker- dark green
a11-rf speaker+ light green
a12-ground black

b1-battery hot-clock-orange
b2-ignition hot- yellow
b3- battery hot-cd
b4-dimmer from dash lights-gray
b5-empty
b6-empty
b7-empty
b8-lf speaker+ tan
b9- lf speaker- gray
b10- rr speaker- light blue
b11- rr speaker+ dark blue
b12- park lamp input- brown

 

I know when I installed an aftermarket stereo in my granddaughter’s 2002 Oldsmobile Alero I had to add a power wire from the fuse panel to make it work. That was several years ago and I used an aftermarket install kit, I looked online and found that many GM car stereo’s were modules and powered through other modules. The factory speakers worked in that install.
This was in an Oldsmobile not a Saturn. I have only used factory radios in my Saturn restorations.

 

I took my volt meter to it and I'm getting 12 volts out of the constant, switched, and what I'm assuming is the dimmer.
I'll take a look at the position for the amp output mentioned on the 2002 diagram and see if theres the same on ours.
Thanks for posting that!