The laptop is run off a standard 12V DC laptop power supply (16V output for Thinkpad). The power supply runs all the time (even when the car is off). That way the laptop can be powered in standby. The current draw when the laptop is in standby is very low (I measured 350mA), this should be ok for a couple days.
The laptop goes into standby when the key is off. I wrote a small VB app that monitors the COMM port DTR pin which is connected to the normal switched radio power (which goes off when the key is off). The VB app monitors the DTR pin and puts windows in standby when that pin goes low (car turned off).
The COMM RI (ring indicator) line is also connected to the radio power. When the car is turn on, the RI pin goes high and windows wakes up. This is an option (Wake on Ring) in windows.
If anyone is interested in a VB app to shutdown via COMM I would be happy to share it.
Because standby still uses vehicle power when the car is off. I will be developing a more sophisticated VB app and associated electronics that will monitor the car batt voltage and automatically put the laptop into hibernation when the voltage drops too low.
O, the display is simply connected the switch radio 12V power.