What Causes a Car's Electrical System to Suddenly Stop Working?

Lights Out, Radio Dead and Engine Shut Off? Here's What to Check

dashboard and road
If your electrical system cuts out while you're driving, the dash lights will die, the radio will shut off, and the speedometer may even go to zero. Images by Fabio / Moment / Getty

Electrical problems can be some of the toughest nuts to crack when it comes to automotive diagnostics, even when the car is available to get hands on with, but there are really only a couple of potential issues that could cause a car’s electrical system to totally shut down and then suddenly start working again. If you haven’t done any diagnostic work at all, and you’re comfortable checking out a few basic things, then you’ll want to start with the battery.

Loose battery connections can cause an electrical system to “shut down” and then start working again, as can bad fusible links, so the connections between the battery and the rest of the electric system should be checked out thoroughly before anything else. Other than that, a problem with the ignition switch can also cause this type of problem. If the problem runs any deeper than that, then a professional will probably have to take a look at the vehicle.

Breaking Down What Went Wrong

In modern gasoline and diesel vehicles, there are two “sources” of electrical power: the battery and an alternator. The battery stores power and uses it to perform three basic functions: starting the engine, running accessories when the engine is off, and powering the alternator’s voltage regulator. The purpose of the alternator is to generate electricity to run everything from your headlights to your head while the engine is running. This is why adding a second battery provides you with more power when the car is off and upgrading to a high output alternator helps when it's on.

If you’re driving along, and everything suddenly goes dead—no dash lights, no radio, no nothing—that means that power isn’t getting to any of those components. If the engine itself dies as well, that means the ignition system itself isn’t receiving power either. When everything suddenly starts working again, that just means that the momentary fault has passed, and power has been restored. But what can cause the power to be cut off like that?

Bad Battery Cables and Fusible Links

The battery connections should always be the first suspect in this type of a situation, both because they are the likely culprit, and because they are relatively easy to check. If you find a loose connection on either the positive or negative cable, then you will want to tighten it up. If you notice a lot of corrosion at the battery terminals, then you may want to clean both the terminals and the cable ends before tightening everything up.

In addition to checking the connections at the battery, you can also trace both the positive and negative cables to make sure that things are tight on the other ends as well. The negative cable will typically bolt up to the frame, so you’ll want to check for rust and make sure the connection is tight. The positive cable will typically connect to a junction block or main fuse block, and you can check those connections as well.

Some vehicles use fusible links, which are special wires that are designed to act like fuses and blow in order to protect other components. These are necessary and valuable components in the situations where they are used, but the issue is that fusible links can become brittle and somewhat less than pliable as they age. If your vehicle has any fusible links, you may want to check their condition, or just replace them if they are old and haven’t ever been replaced, and then see if that fixed the issue.

If the battery connections are fine, and you don’t have any fusible links, there are situations where a bad main fuse could cause this type of issue, although fuses typically don’t fail and then just start working again like magic.

Checking the Ignition Switch

A bad ignition switch, another likely culprit, although checking and replacing one is a little more complicated than tightening battery cables. The electrical portion of your ignition switch will typically be located somewhere in the steering column or dash, and you may have to disassemble a variety of trim pieces to even gain access to it.

If you are able to gain access to your ignition switch, then a visual inspect that reveals any burnt wires is indicative of the type of problem that can cause a vehicle’s electrical system to suddenly cut out and then start working again. Since the ignition switch provides power to both accessories like your radio and your vehicle’s ignition system, a bad switch can definitely cause both to suddenly stop working. The fix is to simply replace the bad switch, which is usually pretty easy once you’ve done the work of gaining access to it in the first place.

Checking the Battery and Alternator

Although this type of problem typically isn’t caused by a bad battery or alternator, there is a small chance that you’re dealing with an alternator that’s on its way out. The issue would be that the alternator isn’t living up to its rating anymore, which causes the vehicle’s electrical system to run solely on battery power until the battery is dead and everything shuts off. In rare cases where the alternator then starts working a little better, the electrical system may appear to be in good working order again.

Unfortunately, there aren’t any really easy ways to test a charging system at home. Your best bet, in this case, would be to take your vehicle to a repair shop or a parts store that has the necessary equipment to load test your battery and check the output of your alternator. If the alternator is no good, then replacing it—and the battery, as running a battery dead repeatedly can cut its life short—may fix your problem.