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Opening a car door should be like opening your refrigerator. A light should come on and stay on until you close the door. This doesn’t always happen, though, as you can attest if your interior lights are on the fritz. Here’s the fix for three common car interior light problems.

1. Dim and Dimmer

An increasingly dim interior light could mean a couple of things: battery or alternator problems. To find out which you’re dealing with, try attaching a multimeter to your vehicle’s battery terminal, while the car is running. This will tell you whether your voltage is normal or low. A low reading is a sign that the alternator needs to be replaced. Remember: A failing alternator can harm your battery, so acting quickly can prevent one repair job from becoming two.

The most common cause of a dim car interior light is a dying battery. It’s also the quickest to solve. Learning how to replace a car battery is, in most cars, pretty simple. However, if your battery is difficult to access, or you’re concerned about safety, have your local NAPA AutoCare install it for you. Auto shops can often even recycle the old battery — an added bonus for Mother Nature.

If the alternator is causing your car interior light problems, you should also replace it before it causes bigger problems down the road.

2. Feverish Flickering

There are a few issues that can cause your interior lights to flicker. First, check to see if you have loose ground wires. Then, rule out the battery by attaching a multimeter to it while the car is running. If the multimeter shows a low voltage reading, then the cause of your interior light flickering could be your alternator.

Another common cause of an interior light flickering is the voltage regulator. The test for that is similar to the test for the battery and alternator, but a little different. With the transmission in park, have a friend rev your car a few times, increasing the intensity each time, while you keep an eye on the multimeter attached to your battery terminals. The voltage should stop somewhere around 14 volts. If the voltage climbs beyond that as the revs increase, then the voltage regulator needs to be replaced.

3. Lasting Light

If the car interior light simply won’t turn off, then check the switch. It may have gotten bumped accidentally by a passenger, valet or car wash employee. If the switch is in the “door” or “off” position and your interior light still stays on, then you should consult a mechanic. There are a few issues that could cause this, and a lot of them involve complex, interconnected systems.

A malfunctioning interior light isn’t just an annoyance. It wears on your car battery and can reduce nighttime visibility, so make sure to take care of the problem right away.

Check out all the electrical system products available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on car interior light problems, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

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