Car ignition off. Some vehicles may require that the ignition switch be in the ON position in order for the power to be supplied to the cigarette lighter socket. If your vehicle does not have a cigarette lighter, fresh batteries need to be installed in the unit. Is your unit functioning properly.
Car voltage converter loose connection. Plug the car voltage converter securely into the cigarette lighter socket and have the DC plug fully inserted into the 4.5V DC socket of the unit.
Car cigarette lighter socket malfunction. The car cigarette lighter socket may be defective. Consult your auto mechanic.