In this post, we are going to discuss and tackle the number one question people, especially those new to car audio, have after they install their aftermarket car audio system. And, that question is, “Why do my headlights dim when the bass hits?” Dimming headlights will probably be the very first thing you notice differently about how your vehicle functions after installing a fairly big audio system, so let’s take a look at the main reason this may be happening.

Dimming headlights is one negative effect of the added, sudden current draw your amplifier needs to produce those low, loud bass notes. If your vehicle’s electrical is in stock form, the system cannot keep its pace with this current draw and the drop in voltage will cause the headlights to dim when the bass hits. If your amplifier has a bass knob with a voltage meter, like the D4S JP series amplifiers, or you have a stand-alone voltage meter, you will probably witness the voltage drop as those bass notes play. 

If you search other blogs and forums, you may notice a lot of people suggesting to just add a second battery. But, in reality, this may be more detrimental to your situation. Adding a second battery sounds good, in theory, but what you are actually doing is adding more strain to your already tired alternator. Plus, the second battery may be good for a few bass hits, but as its reserve power begins to deplete, it takes time to charge back to its peak performance, thus leaving your headlights dimming again. 

The fact of the matter is, your alternator is not designed to feed today’s car audio amplifiers. They are designed to barely run the stock accessories. In a previous post, I discussed why your stock alternator needs to go in the dumpster and be replaced with a good quality high-output alternator. You can read more about alternators HERE. But, if you don’t feel like it, let’s review. Your alternator, in stock form, is only feeding your power-hungry amplifier between 40% – 50% of its rated maximum amperage. So add in the headlights, A/C, and other accessories, and your stock alternator just can’t cut it. 

Now, there are a few things you can do to remedy the dimming headlight situation you are in. The first recommendation I would give, replace your stock alternator with a good-quality high-output version. Purchase the highest amperage alternator you can afford. There’s no such thing as going too big here. In my opinion, bigger is actually better. Buying the largest high-output alternator you can will not only give you the power supply your electrical and car audio systems need, but it will also give you the room necessary to upgrade to a bigger amplifier or run multiple amplifiers later on down the road. 

Secondly, you can run a capacitor, IF you cannot afford a high-output alternator. Now, you will definitely catch some flack for using one of these. A lot of people will swear they don’t even work, and there is some agreement here. But, it also depends on how big your amplifier is. If you are running a Crescendo Audio BASS CLEF 17K, then a capacitor won’t help, but on the other hand, if you have something like a Skar Audio RP-800.1D, then I’d give a capacitor a try. The capacitor will act as somewhat of a buffer between your amplifier and the stock electrical system. A capacitor can add a quick jolt of power for your amplifier when needed, but unlike a second battery, a capacitor can be recharged very quickly to have the reserve power ready for the next bass drop. 

Thirdly, and not a car audio fix by any means. Replace the headlight bulbs. If your vehicle is equipped with traditional halogen bulbs, try replacing them with LED versions instead. The LED bulbs require far less current to operate than the halogen versions, which should eliminate your dimming issue. But, keep in mind, this is not actually fixing the true problem with your vehicle’s electrical system. You are basically just using a bandaid at this point.


I hope you found the answer to the question “Why do my headlights dim when the bass hits?” This post was intended to give the newbie in car audio, the easiest solution(s) to fixing the headlight dimming problem. Use the LED bulb suggestion and the capacitor suggestion as only a temporary fix. The alternator is key to a healthy electrical and car audio system.


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About The Author Brandon L

comments (1)

  • I would also recommend checking your headlight bulbs. old bulbs will draw more power than newer ones, checking the state of your headlight lens. a faded headlight lens may reduce the light reaching out when they take a hit to power supply and make it look like a bigger hit than it really is.

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