2003 gmc sierra wiring harness

I'm very confused, my adaptor and stereo harness both have red, yellow, blue and black. However, the harness in the truck only has the ground and two orange wires, one thicker than the other. I believe this is the hot wire, but not sure. Either way, this wire is connected to a pin that does not associate with any wire on my adaptor or stereo harness. The stock radio stayed on when ignition was turned off until door opened, however I do not see a trigger wire on the truck harness either. Could this radio be one with a subwoofer behind the glove box? (I read a few things about that possibility) When I plug in my adaptor harness to the truck harness, it fits perfectly, the red light under the face plate flashed constant but that's it. Nothing else. Thanks in advance for any advise, diagrams and/or simple instructions you could give me (trying to prove to my negative husband I can do this)

ok, update...just did the test to identify wires (very cool by the way) and my larger orange wire is the only one with 12v with the ignition off (no key in) and when in run or aux position. that doesn't seem possible, Now I'm more confused

Did you already HACK the plug off the factory harness?

My guess is yeah...

those trucks do not have a switched power feed in the harness for the factory radio, its all done with data. there is a plug which retains the ignition feed and keeps the radio on until you open the door. it also retains all warning chimes that come through the drivers speaker. if you are just wanting to match the wiring from the factory plug to the after market radio then im afraid its a little harder than that.