My setup uses a usb cable that I cut the end off, plugged it into my unpowered usb hub, and wired to a relay to "throw the switch" on my accessory, or car pc power line which includes the computer(a laptop with its own battery), a line to my power inverter (which runs my usb hub power), my lilliput lcd, and a remote lead to my amplifiers.
I wired the lid switch from my laptop to a normally closed relay which gets thrown when they key comes on... in essence "opening the lid" on my laptop which tells the computer to resume from standby. But, sometimes when I shut the key off, the computer goes into standby and the usb stays on, keeping everything on, but other times it will shut right down, everything will turn off, and the standby light will flash on my computer.
I have a powered usb hub plugged into my non powered hub, is it possible it is feeding power back to the hub? Is there anything I go do to force usb to be shut down?