With the unit on, tap the power button to open the status screen. Adjust the brightness slider to max (toward the top). Tap the return arrow in the lower left corner to return to what you were doing.
That said, a lot of people complain that maximum is not bright enough.
I am not sure of the meaning of the comment about USB power while not in the mount. If that is your situation, feel free to PM Garmin-Andrew for clarification.
