Circuit breakers are designed to fail safely before wiring or devices in your car . So if your fuse cigarette lighter continues to burn out again and again, this is a very good indication that there is some type of underlying problem that needs to be addressed. The problem could be with the cigarette lighter socket, with the device you are trying to connect, or even with the cigarette lighter wiring.

The only way to fix this so that the cigarette lighter fuse stops blowing is to check every possible point of failure until you identify the problem. But whatever you do don’t even think about replacing the cigarette lighter fuse with a big amp fuse . Depending on the nature of your problem, replacing a fuse with a higher amp version may damage the fuse box, melt wires, or even cause a fire.

How do lighters work?

Car lighters are simple devices that have changed little in decades. The two main components are an outlet that connects to both power and ground, and a removable plastic or metal housing that contains a rolled metal strip.

In most cases, the inside wall of the outlet is grounded and the pin in the center is connected to a fusible power source. When you plug a lighter into an outlet, current flows through the twisted metal strip, causing it to heat up.

Under normal circumstances, the cigarette lighter can be expected to draw approximately 10 amps, and cigarette lighter circuits are usually 10 or 15 amp fuses. This allows you to plug in phone chargers and other devices that draw less than 10 or 15 amps, depending on the fuse in your particular car.

To power 12-volt devices and power adapters, you can use both cigarette lighter sockets and special 12-volt auxiliary sockets. So if you have a 12 volt auxiliary circuit socket that keeps the fuses blowing, the diagnostic procedure will be about the same.

Why do cigarette lighter fuses blow?

blown cigarette lighter fuse

What does a blown fuse look like?
Tydence Davis / Flickr / Creative Commons (CC BY 2.0)

Cigarette lighter fuses, like all automotive fuses, blow when the circuit draws more current than the fuse is designed to operate. If the cigarette lighter fuse is 15 amps, it will blow if it blows more than 15 amps. If you replace it with another 15 amp fuse and the current in the circuit is still drawing more than 15 amps, then the fuse will simply blow.

It may seem like the simplest solution would be to simply replace the 15A fuse with a larger fuse, but this is actually very dangerous. Although the wiring in the cigarette lighter circuit can handle just over 15A, there is no guarantee that this is actually the case. And if the problem in your circuit is actually the cause of the short circuit, then turning on a larger fuse could cause the wiring to heat up to the point where it could melt or even start a fire.

While you can buy a circuit breaker as a direct replacement for a fuse that keeps blowing, that’s also a bad idea, especially if there’s a short circuit in the circuit. These circuit breakers are useful in some applications and have certain diagnostic uses, but it is not recommended to use them to deliberately overload the cigarette lighter circuit.

Check for foreign objects in the cigarette lighter socket

There are many reasons for the cigarette lighter fuse to blow repeatedly, but one of the most common and often overlooked is the presence of a foreign object in the socket. Since the cigarette lighter sockets are designed so that the entire body of the metal cylinder is grounded and the center pin is hot, it is surprisingly easy to complete the circuit.

Some cars have interchangeable holders or universal trays near the cigarette lighter socket, making it dangerously easy to drop a coin. In this case, the coin can come in contact with both the grounded case and the hot pin inside. socket and cause a short circuit.

Other metal objects, such as paper clips or even those broken off from old phone chargers, can also become stuck in the cigarette lighter socket. In some cases, you may find that such an object does not cause a short circuit all the time, but when connected to the cigarette lighter or 12 volt power adapter fuse blows immediately.

If you look into the cigarette lighter socket with a flashlight and see a foreign object, there is a good chance that removing it will solve your problem. Just in case, you should make sure that you removed the cigarette lighter fuse before getting inside the socket to remove the foreign object. You can then install a new fuse and see if it’s blown.

Check the device you want to be powered by the cigarette lighter

There is a hard limit on the current you can draw from the cigarette lighter socket or any 12V accessory outlet. If the device you want to turn on with the cigarette lighter draws more amperage, then it’s the simple fact that the fuse blows every time you plug it in.

Most cigarette lighter circuits use 15A fuses, but you can check the fuse box in your car to be sure. Next, you’ll want to check the device you’re trying to connect to see how much current it draws. Cell phone chargers are usually designed to work with cigarette lighter sockets without burning out, but other devices such as cigarette lighter inverters can easily overload the circuit.

Even if your 12 volt device, charger, adapter or the inverter is rated to draw less than 15 amps, it’s still worth inspecting the plug. If the plug is broken, worn, or has something stuck on it, plugging it in can cause a direct short between the power source and ground inside the cigarette lighter socket.

If you’ve ever tried plugging one thing into your cigarette lighter, it might be worth trying a different 12V charger or adapter, just to rule out a problem with the one you were using. Or you can also use ohmmeter to check for an internal short in your adapter.

Problems with the cigarette lighter circuit

In most cases, a cigarette lighter burnout is caused by some external problem. However, it is always possible that you are dealing with an internal problem. If the fuse always blows without even connecting anything, and you’ve made sure there’s no foreign object in the socket, then there’s a problem somewhere else in the circuit.

To completely eliminate the problem with the outlet itself, you can remove it and see if the fuse is blown. This is an application where a circuit breaker fuse can be useful as blowing fuses over and over again to narrow down the source of your problem can become costly.

This type of problem will also be easier to diagnose if you can trace the wiring diagram for your specific vehicle, as it will show you any components other than the cigarette lighter that are also on the same circuit. Disabling each of these components in turn, if any, can also be helpful in determining the source of your short circuit.

Another likely cause for this type of problem is a shorted power wire. Essentially, this means that the power wire that plugs into the cigarette lighter can fray or burn through and come into contact with metal somewhere behind the dashboard. You can find this type of short by checking for continuity between the cigarette lighter wire and ground.

Short circuit detection

Depending on your specific vehicle, it can be extremely difficult to find the location of this type of shorts. The short may be located in a hard to reach position that you can’t find without removing the radio, HVAC controls, or even the dashboard.

Although there are devices for finding shorts in the automotive industry, this is not a tool that will be in the public eye. In some cases, the simplest solution may be to simply leave the cigarette lighter fuse on for a long time and plug a new power cord into the cigarette lighter socket.

Reinstalling a faulty cigarette lighter circuit

If you decide to connect a new power wire to the cigarette lighter socket, it is very important to use the correct test lead. It’s also important to install an appropriate fuse if you decide to go down this route. In some cases, you can use the empty space in the fuse box, and in other cases, the only option is to connect the power cable directly to the battery.

In both of these situations, failure to use the correct fuse can easily result in a fire. And in any case, using a new power wire should be your last resort after you have ruled out any other potential cause of the cigarette lighter fuse blowing again.

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