How to light an LED to indicate when a usb port has a plug in it?

I'm looking for a way to light a 3.0v-3.4v 20mA LED to indicate when a usb 2.0 port has a plug in it. The light should only be on when a device is plugged in. My usb 5v line is about 3.2 to 3.3 amps with an Xbox 360 Controller connected. I tried wiring the led and resistor in series with the 5v usb port. The LED lit but the plugged in device did not work. I'm guessing the LED was only allowing 20mA to the device (Xbox 360 Controller) which was not enough for it.

Hi Matthew,

Its correct that you serially connected the led and the resistor. But I'm guessing that the resistor is a little bit larger in value, since the device didn't work. Just look at this way, to get the resistor value that is just right for your application, you use ohms law. or simply stating that the amount of current is equal to the voltage potential across your load.

I know you can do the math afterwards. I(ampere)=V(volts) /R(ohms)

Best,
Kevin

Lets be clear here, you said you wired the resistor and led in series with the 5 volts.
The way that reads there is no way anything would work. Do you mean that you wired the led and resistor in series and placed then between the 5 volt rail and ground?
cheers,
Richard