The rear USB ports, most likely, are numbers 1-6 and the front panel USB could be any of the remaining #7-14. So, just plug the USB 2.0 into the USB78 connector. Did you already connect everything else for the front panel?
Yes I plugged the molex into my psu that powers the 3 fans+controller and the usb 3.0. All thats left is the usb 2.0 connector, ill take your advice and see what happens thanks.