If you are plugging a phone into the King Meter, turn the bike off, plug the phone into the USB port, and than turn the bike back on. With this plug in sequence I have had luck with phones that didn't want to take a charge from the on-board USB. Hope that helps!
Which bike model do you have? Feel free to email email@example.com if you think you might be in need of a new back light or have any other questions!