I've got a non-navi 04 TL and want to use the Navi version of the steering wheel buttons (HFL/Navi buttons) and use the 2 unused Navi buttons for aux functions (e.g. remote radar mute button, NOS button, etc.).

I've got the electrical troubleshooting guide and it looks like you could possibly tap the signal coming out, but they multiplex the signal with different resistance to indicate which button is being pressed.

Anyone have ideas on how to go about doing this?

 

Haven't had time to go down this route with my carpc yet, but I do know this is how video game controllers and usb devices with multiple buttons typically work.