How to Tell If Headlight Ballast Is Bad?

HID headlights use ballasts in order to get the right amount of electrical arc current and voltage for lighting. If your headlights suddenly stop working or start to flicker, there can be any malfunctions in the ballast. However, it isn’t confirmed until you check the system and find out whether it is the real culprit or not. It can also be a faulty headlight relay causing the trouble.

After going through this article, you will find different symptoms of a bad ballast and ways to confirm if it is faulty. Doing so can let you decide whether to spend money on a new ballast, other parts, or the whole system.

What Is a Ballast?

The ballast is a component of a high-intensity discharge system (HID) that acts as a voltage and arc regulator. Unlike the heated filament method in traditional incandescent and halogen bulbs, HIDs use electricity arcs to jump between two electrodes to generate light. HID lights require a specific voltage to keep the bulb working perfectly. Your vehicle’s battery only provides around 12V to the headlights, which is insufficient for an HID bulb. So, the ballast helps here by increasing this voltage to the correct amount. So, if a ballast goes faulty, the bulbs will show some symptoms. In fact, it can damage the HID bulbs completely.

Symptoms of a Faulty Ballast

As mentioned above, you will notice some signs when your ballast goes bad. Note that some of these symptoms can also happen for other reasons, so you should check the ballast. Anyway, let’s look at them below.

Dimming or Flickering Bulbs

The primary sign of a faulty ballast is seeing your headlights flickering or dimming. When the ballast can’t function properly, it fails to provide the necessary voltage to the bulbs, making them dim or flicker. Although, it can also happen when your low beam bulbs are bad.

Bulbs Not Working

If you notice your headlights are not turning on when you are trying to do it, the reason can be anything. So, check for a loose wire connection or installation. Also, check if the bulbs are okay. If everything seems all right, the faulty ballast can be the one causing the inconvenience.

Color Temperature Fluctuations

If the ballast goes faulty, it may not be able to provide the correct voltage needed for the bulbs. It can cause a voltage fluctuation. In this scenario, you may see the bulbs losing their whiteness or going brighter and whiter for a short period. If it continues, it can damage the bulbs. It is not unusual to happen for old ballasts.


If the ballast cannot regulate the voltage well, it can make buzzing sounds. You may also hear it when the headlights are off, indicating that the ballast is still working when it is supposed not to.

Frequent Fuse Blowing

A malfunctioning ballast can cause your fuse to blow frequently. As a result, you will have to replace the fuse occasionally. If it happens, check the ballast for any potential issues in it. Basically, the failure of voltage regulation led the ballast to increase the electrical current, resulting in blowing a fuse.

Directly Observe and Check Your Ballast

While the previous points are symptoms of a faulty ballast, they do not confirm anything. You need to check the ballast directly to find the culprit for sure. If you see your ballast in the following states, consider replacing them.

Bloated or Damaged Casing

If you notice the casing of your ballasts in a bloated state, it can be because of too high voltage. Therefore, you indeed need to replace the ballast. However, before putting the new one, check the fuse and the power source for any potential problems and troubleshoot them. Otherwise, even the new ballast may get damaged soon.

Vapor and Oil Damages

Finding oil and condensation inside your ballast can indicate it is not all right. Replacing it is the best solution to prevent shorting various parts of your vehicle’s lighting.

Burn Marks

The capacitor has likely blown if you notice burn marks inside the ballast. When it faces too high a voltage, it usually bloats and blows. Having a blown capacitor is not unusual considering their duty of voltage regulation. If this part is burnt, you may only replace it instead of the entire ballast, and it doesn’t cost much either.

Final Note

Having your headlights flickering or dimming at nighttime is a heavily annoying moment. If it happens, do not ignore it. Check the symptoms and the ballasts directly. If you find any issues in the ballast, replace them with new ones. But before you install them, test the power source and the fuse. If they are faulty, even adding a new ballast will not solve anything.

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