Just wanted to share some info on installing a Pioneer AVIC-F900BT GPS/DVD in my 2008 Impreza WRX (non-nav). It took a fair amount of searching for these detail so I hope it save some trouble for others:
Antenna - just plug in the factory plug into the back of the deck, no adaptor needed.
Subaru 20 pin connector pin out:
1 = GRND
2 = violet (+12 with lights on)
3 = Black/White (Dimmer)
4 = yellow/red (+12 accessory)
5 = Brown (steering wheel controls)
6 = red/black (speaker LR)
7 = white/red (speaker LR)
8 = white/black (speaker LF)
9 = blue/orange (speaker LF)
10 = yellow/black (power antenna)
11 = green/red (????)
12 = pink (????)
13 = none
14 = yellow (steering wheel controls)
15 = red/white (speaker RR)
16 = gray/green (speaker RR)
17 = green (speaker RF)
18 = brown/yellow (speaker RF)
19 = none
20 = +12 constant (i.e battery)
Pioneer Color Code
white = LF Speaker +
white/black = LF Speaker -
green = LR Speaker +
green/black = LR Speaker -
gray = RF Speaker +
gray/black = RF Speaker -
violet = RR Speaker +
violet/black = RR Speaker -
black = GRND
yellow = +12 const (battery)
red = +12 accessory on
orange/white = +12 with lights on
light green = parking brake (to GRND if you wish to defeat restriction on watching video while in motion).
pink = speed signal input (I didn't connect this and everything seems fine)
violet/white = reverse gear signal (I didn't use this one - as I don't drive backward and try to use the gps at the same time).
yellow/black (upper row left on the second harness - the one with all the RCA plugs) = Audio Mute (if you move the pin in this connector to the empty space on the lower row 4th space from left and then ground this wire (and the light green parking break wire) you will have the ability to use all functions while in motion. Of course none of you would do this in an Impreza but you could.
Steering Wheel Controls:
Use a PESWIPS Interface (got mine at Fry's)
Follow the Nissan 2008 Pathfinder Instructions
Black to GRND
Red to +12 accessory
White to pin 14 yellow on subaru radio harness
then ground pin 5 brown on the subaru harness
You don't use any of the other wires.
Connect output of PESWIPS to the jack on the back of the deck.
Program the buttons as per the instructions.
Hope this helps someone.