2008 silverado switched 12v wire

I'm putting in a Clarion In-Dash touchscreen (flip-out) in an 08 Silverado Crewcab. The Metra harness specified is the same as a Chevy Aveo of the same year (the owner doesn't want to pay for the $150 metra harness that retains all the factory door chimes/warnings) - the factory harness doesn't have a switched 12v for ignition turn-on of the head unit. The metra harness comes with a separate red lead to use for your switched, and just instructs to patch into the fusebox on another switched circuit. This is a base model truck with manual windows, black rubber/vinyl floors, no privacy glass, etc. There are NO switched 12v circuits in the fuse box that I can locate - the only ones that aren't constant 12v are the power lock/unlock circuits (4 of them if I recall). Where else should I look for a switched power wire? Can it be done without wiring in a relay?

You need a relay and can be found at the ign switch.

You might want to check your local laws though about removing safety devices. In my state, it is a federal offense and the highest I believe they can charge you is 2nd degree manslaughter if the person is killed in an accident. I personally would not even touch the vehicle without the specific harness for that reason.

Also his blinker clicks won't work without the lan harness. Other stuff is:

blower motor speeds
low oil level
low gas
key left in IGN chime
Seatbelt chime
lights left on chime
RAP
Check engine light

That's pretty important stuff IMO.