2500hdtyler

Okay so i just bought this truck and it had an aftermarket stereo already in it, i had a differnt and much nicer one i wanted to install i picked up the wireing harness from a local autoparts store and plugs in fine, i have done a couple of these but this one has me confused.
I hooked up all the speaker wires correctly the only problem i am having is that idk what to hook up the the,
dash/illumination light
or
the 12v ignition switch wire, they also gave me a longer extra 12v ignition wire in the package and im unsure on where to wire it in or up too, can anyone please help thank you.

2004,2500hd ext cab.