We are trying to use a spare USB3 port on a PC to drive an LED as an indication that the PC is powered ON. The PC has a power on LED but it's in a rack and is not visible to the operator. We have connected the LED across the USB3 VBUS and USB 3 GND pins and have discovered that it doesn't work. We believe however that it would work with a USB2 port (as I have found numerous articles telling me how to get 5VDC from a USB 2 port by simply connecting the red and black wires to whatever we wanted to power). Can anyone please confirm that USB3 operates differently ? Our tests would suggest that the power isn't available unless the PC detects the presence of a device connected across the data pins. If this is the case can someone please advise if there is a simple way to trick it to believe that there is a something there ?