Advice for using external USB module

Thanks in advance for any advice
I have a Pixhawk and trying to use external USB/RGB module that came with this unit, the external RGB works fine, but the external USB is not recognized by the PC when I attach usb cable?
Does the Pixhawk have to be powered to use this external USB unit?
This USB unit only has a 3 wire connection, some units have 4 wire connection, do not know if this is problem?
Attached is a pic of USB/RGB

You are correct, the USB should have 4 wires.

Pwr, D+, D-, Gnd

Looks like a bodgy unit or they have just left 1 wire off the cable, or the cable is the wrong way round.
It is usual for the I2C to have only 2 wires, using the Pwr and Gnd from the other cable.
This usually the case with the I2C compass in a GPS, or the RGB LED in one of these units.

Thanks again
Found out the unit works with the 3 wire hookup for the USB, plug in to USB and 12C port, power the Pixhawk, everything is working?
When I plug in USB cable the remote led module get dim, is this normal?
Is this a problem to have power module and remote USB both powering the Pixhawk?