Basically a switch on the ACC line (or IGN line). That would be the switched power line that runs to the Opus that tells it when to boot up or shut down the PC.
By putting a switch on this line, you can manually turn the PC on/off with the switch. It would control the power on the ACC line, which is what the opus uses to trigger startup/shutdown. If the PC is on and you turn the switch off, then the Opus will trigger shutdown (or hibernate or standby, as appropriate).
If the PC is off (and the ignition is hot) and you turn on the switch, the PC will boot up.
the other benefit is that you can turn the switch off if you're having a valet park your vehicle, then the PC will stay off, preventing them from messing with it.
