Can the buttons on the steering wheel be hijacked for other purposes? Does each button have a physical connector? Where are they? Does each button control +12v (on)?
No they (at least stereo buttons) work by changing resistance between two wires. Most of car stereo wired remote controls work like this. In Prius one wire is ground and you have two signal wires. Wire one has (at least) seek+, seek-, vol+ and vol-. They have resistances to ground: Nothing pressed more than 100Kohm seek+ less than 2.5ohm seek- about 0.3Kohm vol+ about 1Kohm vol- about 3.2Kohm Wire two has at least mode. They have resistances to ground: Nothing pressed more than 100Kohm mode less than 2.5ohm Simple circuit can be build that (for example) connects to wire one, ground and power and has separate outputs for seek+, seek-, vol+ and vol-. Connections are probably easiest to do behind stereo and you need to disconnect the wire from stereo since you dot want it to read buttons if you use them for something else.
