Not all rental cars will include the option for a cigarette lighter that works by default. This is usually because the companies do not want people to smoke in rental cars which could cause lasting smell to occur within the vehicle and extensive cleaning to ensure that it does no longer smell of smoke. Even though some people are not smokers, they may need access to the cigarette lighter port of the vehicle for other devices such as cell phone chargers as well as GPS and other devices.
The simple way to ensure that the cigarette lighter is functioning is to ask the employees of the rental company if the cigarette lighter port is disabled. If they answer yes, ask if they can enable it for use to help power your devices through your adapters. This may cost an extra fee, simply because they are not sure if you would use the cigarette lighter to light up cigarettes and cause them extra cleaning and deodorizing later when you return the vehicle. They may even refuse or say that the feature is simply excluded because it is not integral to the rental vehicle.
Connecting the cigarette lighter on your own could be troublesome if you do not know what you are doing. One easy fix could simply be that the small fuse that is meant to be used for the cigarette lighter was removed which will cut the power supplied to it when you try to use it. Getting the appropriate fuse and putting it into place will usually do the trick. Depending on the type of vehicle and whichever company you are renting from, this may not even be an issue. Just make sure to ask about it before it is too late and you are already on your trip!