CD changer install

Alright, I'm finishing up installing a cd changer (Pioneer fm-modulated) in my friends Firebird (98 3.8) and I have a question. There is a red wire that needs to be hooked to an electric terminal controlled by the ignition switch. Where can I connect this to on his car?

Thanks

I connected mine to the power supply on the radio harness. Just tap into it. Not the constant 12v. You're gonna be in back of the radio anyway.