I wanted my factory steering wheel audio controls to work with my Clarion DVD head unit. This is what I used.........
PAC (Pacific Accessory Corp.) makes mobile audio interfacing equipment. I used there universal steering wheel control interface unit that works with the aftermarket head units remote control (SWI-X). There are other models that are either vehicle, or head unit brand specific. I got lucky that I could use the universal kit!
It's hard to see,but you tap into the factory harness.....
See the interface just above the ATX shifter.....
Where I mounted the interface remote control eye.....
Full control over the aftermarket DVD player via stock steering wheel controls.....
It even controls my video ipod when it's hooked up to my head unit.....
It works great. All my audio controls on the steering wheel now is interfaced with my Clarion DVD deck, including my iPod, when it's connected.
Volume up and down, mute, source, skip, replay, preset channel up and down. This thing is cool.