This is something I plan to do to this project with the simple serial circuit that the first post refer to.
There are 3 inputs and 2 outputs pin on the serial that we can use. I have them all figure out but didn't have time to put together.
One input can be fore video safety switch (ebrake), one for software SDC (ACC/IGN switch), and another for light control (headlight/photo sensor switch). My Matrix has auto-on head light so I want to take advantage of it.