I am not totally for sure but I think pioneer and sony are the only two brands that make a special wiring harness for the gp with steering wheel controls. I know mine works I have a pioneer but it isn't a disc changer. I was lazy and I had professional install on it. I will call them and find out who makes that special harness when I get a chance.
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"driving fast is just a way of life officier"
mods: tinted windows (mirror to black), silver headlamp covers, 2 12in pioneer premiers, pioneer prmier cd/mp3 player, alarm system with car montioring and pager,CAI and thermostat, blue stripes, blue badging. Look for a quick hp increase.