I'm going about creating a steering wheel interface for those of you with Pioneer radios that have the wired remote input.
This is the information about the wired remote:
http://jvde.net/node/7
Here are the resistances you get from the audio controls on the wheel (tested, but these are also from the service manual). Measure between pins 1 and 2 on the audio control pad itself:
71 kOhms = Nothing Pressed
270 Ohms = MODE
740 Ohms = CH UP
1.3 kOhms = CH DOWN
2.1 kOhms = VOL UP
3.1 kOhms = VOL DOWN
4.6 kOhms = SPEECH
6.3 kOhms = OFF HOOK
8.6 kOhms = ON HOOK
They are supposedly routed to the radio on pins 2 and 12 of the main audio harness, but I have not tested that. The service manual does indicate they arrive unmolested there.
I have attached the circuit I plan to build. Sorry for the extremely ugly diagram, I've never used kicad before so... uhhh... still learning. I'll let you all know how well it does or does not work. And I'll add in any significant changes I make (you can set your own choice of output resistors to do any radio functions you like).
As far as I can tell, this should work for any Pioneer stereo that has a 3.5" headphone jack labelled "W/R".