I just bought a head unit from a friend of mine, but not brain or wiring harness. I'm confused as to whether or not I need the brain to operate the cd player, I have a 2000 Honda Accord Coupe, and I've seen a lot of things saying that I have to have the brain unit to operate GPS capabilities only. But I've also been told that I have to have the brain unit to operate anything on the Cd player, that it won't even power on without it, I haven't bought anything yet because I don't want to spend the money on the brain unit unless I have to atm, I might get it later on if I can, but it isn't necessa