Okay, so some more research will be needed, I do not recommend cutting anything, like the others said because you will lose onstar and possible airbag failure. There are adapters for all these mechanisms to work with your radio but they are pricy.
If those aren't much use to you, then here is some help.
Most of the wires you will need are within the black plug.
12V power + (red/white
12V power - (black)
Dimmer (yellow)
FR + (light green)
FR - (dark green)
FL + (tan)
FR - (gray)
RR + (light blue)
RR - (dark blue)
For some reason, the LR speakers as well as the amp wires are in the yellow plug.
LR + (brown)
LR - (yellow)
Sub + (blue)
Sub - (blue/black)
That just leaves the one green wire in the black plug (#13 I believe)
This wire, if you connect it places you will see you loose lights in some places, and airbags in others. So I really do not know what to do with this plug as supplying it with voltage hurts the system somewhere else but not having it plugged in leaves something behind.
ALSO, newer GM vehicles don't have an accessory wire so on your radio, you must take that and run it thru your truck to wherever has 12V with key on only. This will be the culprit if your radio not having power or light on the screen. But has lights on the buttons.
With all that, after hooking up, it seems that onstar is no longer green, (maybe its that green wire?) But that aside the radios work for these trucks without any wiring harnesses.
Although If your friends plan to upgrade, suggest to them the intellilink from newer gm models as it is almost plug and play in most cases.
