The orange wire (A) on the wrx harness goes to the orange/white wire (D) on the pioneer harness, this is optional though, only if you want the screen and buttons on the pioneer to dim down when you turn your lights on.
The blue wire (on the wrx harness) I don't recommend using. On cars with a motorized antenna, some people will connect the amp turn on lead (blue/white wire) to this wire since pioneers don't have a true power antenna wire, but our cars don't have a motorized antenna. I'm not 100% sure, but I think that wire may be used to power a stock antenna booster (if there is one), and if so it may require more current then the pioneers turn on wire can provide. if you actually listen to FM radio you may want to try connecting this wire, I usually don't bother with mine.
The green parking brake wire, this is SUPPOSED to be tapped onto to the wire that comes from your parking brake that tells your cars computer that the parking brake is engaged. this is the LEGAL way to do it, and your pioneer unit will only display video when the parking brake is engaged. If you want to watch video while driving PM me and I will explain how.