hi Legend-ary,
I don't remember 3 wires, but all I did was pull the entire radio out with all the wiring at the back still attached. I couldn't entirely get the whole unit away from the car as I didn't want to unplug anything, but I had enough space to plug in the USB adapter and feed the cabling round to the glove compartment.
You say you have an 03 - just check that your radio unit accepts the port. My unit is the later model with the large LCD screen and large volume knob to the right.