button starter kill

Typically steering wheel buttons are analog - each switch is a different resistance and depending on which switch (or whal all switches) are pushed the voltage going back to the controller will change.

A few years ago I converted a guys "fan up" and "fan down" steering wheel buttons on his Caddy in to paddle shifters (it was a STS with a single turbo on it).  What I did for that was used two op amps per button and set them up as comparators.  I measured the voltage for each button (say 2.5vdc and 3.5vdc).  I then set the comparators up to have "windows" in them (like a bandpass filter) that were just big enough to work reliably.

In the end, basically, I had two seperate comparators for one button that turned on when the voltage was above 2.4vdc / below 2.6vdc respectively.  I then took those two outputs and ran them through an AND gate (I believe) so they both had to be on - and if they were both on the output of the AND gate turned on.  The AND gate could be setup to drive a transistor that would drive a relay that could act as the starter kill. 

A switch that is a digital (ie on/off) switch would be better then an analog switch.  Most seat switches are digital.

However, remember when you crank the car your seat will be moving!