Why Doesn't My 12v Socket Work?

Shouldn’t I be able to use my cigarette lighter to plug in 12v stuff?

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Since all cigarette lighter sockets are also 12v sockets, you should be able to plug in an cigarette lighter inverter, cell charger, or any other 12v DC accessory and have it work just fine. There are a few things that could be going wrong, and it’s tough to say exactly what the problem without knowing whether it is a pre-existing issue, or if it started after you plugged in the inverter.

Essentially, there are two things that could be wrong. Either the cigarette lighter fuse is blown, or there is some kind of problem with the actual socket that is preventing your accessories plugs from making good electrical contact.

Check for Foreign Objects

In a situation where nothing you plug into a 12v accessory socket works, the first thing you'll want to do is check for obstructions inside the socket. The easiest way to do this is to grab a flashlight and physically look inside the socket.

One of the most common causes of cigarette lighter and 12v accessory socket problems is when a coin falls into the socket accidentally. This can cause the socket to short circuit and blow out the fuse, but it can also prevent accessory plugs from making contact.

When non-metallic objects fall into a cigarette lighter or 12v accessory socket, you won't end up with a short circuit or blown fuse. However, the foreign object can still prevent an accessory plug from making electrical contact. That means the circuit will still be hot when you reach inside to remove the instruction, so take care not to accidentally short it out.

Check for Power

If there aren’t any obstructions in the socket, then you can proceed in one of three ways. The easiest is to simply plug in the cigarette lighter if you have it. If the lighter heats up and pops out, then the socket has power. You can also use a test light to check for power, if you have one, or examine the fuse panel to see if the cigarette lighter fuse is blown.

If your 12v socket is actually an accessory socket, and not a cigarette lighter socket, then you can't test it by using the cigarette lighter. In that case, you'll have to use a test light or multimeter to actually check for power.

If the fuse isn’t blown, and the socket has power, then there may be an issue with either the socket or the accessory plug that you are trying to use with it. Cigarette lighter and 12v accessory sockets are designed with somewhat loose tolerance in mind, and the slack is taken up by spring-loaded contacts, but if contact isn’t taking place, then your accessory won’t receive power.

Dealing with a Blown Cigarette Lighter Fuse

In many cases, you will find that the fuse is blown, which can be the result of a number of different issues. If you found a coin in the socket, then that is probably the end of it. If you didn’t, then you may have a short elsewhere, or the cigarette lighter inverter you plugged in may have drawn more amperage than the circuit is designed to handle.

Cigarette lighter circuits are often fused at 10 or 15A, which isn’t a whole lot in the grand scheme of things. So if your cigarette lighter inverter isn't specifically designed to keep current demands below that level, plugging in any number of electronics could theoretically blow your fuse and keep the inverter from working.

The easiest way to proceed from there is to replace the cigarette lighter or 12v accessory socket fuse and see what happens. If it blows immediately, you’re dealing with a short somewhere in the circuit. If you plug in the cigarette lighter and the fuse blows, then that is probably the issue. If everything is fine initially, but the fuse blows when you plug in the inverter, then the inverter is probably the culprit.

In any case, the inherent limitations of cigarette lighter inverters mean that you may end up better off with a different inverter that is hooked either directly to the battery or to the fuse panel. For more information about that, you can check out how to estimate inverter requirements