Sorry Sonic, I dont know what you mean by 'You connect them'. Do you mean to each other so that Green is grounded? And then control the ON/OFF state of PSU via ignition state and inturn control on/off state of the odroid with the Blue remote wire (via a relay to the 5v rail)?
yes, splice/jumper the green and black together and tape/solder it. It basically tricks the power supply into thinking a motherboard is connected. With that connection established, the remote wire becomes the on/off trigger for the system. If you have a backup battery and want to leave the ODROID running until the PSU detects low voltage state, just connect remote to your 12v line. If you want the ODROID to turn off with the car, connect the PSU how the instructions state.
Either way you have to keep in mind that there's no way to trigger a "graceful" off for the ODROID. This really doesn't matter though, I haven't had any problems with just pulling the plug on the ODROID for over a year now.