Most cars are equipped with cigarette lighters that serve a dual purpose--to light a cigarette and power various types of accessories while you are driving. Like the other accessories in your car, the lighter gets its power from the car battery, so make sure that your battery is strong enough to power and start the vehicle.
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Make sure that your accessory is equipped with a cigarette lighter adapter. This is a circular, bulb-shaped unit that has a metallic pin on the end. Common accessories that have these adapters include radar detectors, cell phone chargers, MP3 players and GPS devices.
Remove the burner unit or cap (comes standard in most cars) and plug the accessory's adapter into the lighter.
Start up the car. You may also be able to simply put the ignition into "Accessories" mode as well in some vehicles to send power to the lighter.
Turn on the accessory and use it as needed. If it's a cell phone charger, plug the other side of the cord into your hand-held device. Keep in mind that when you turn off the car and remove the keys from the ignition, the accessory will switch off automatically, so save any settings on the device first.