Why are my headlights dimming when the bass hits?



Headlights dimming when the bass hits is a common problem for the do it yourself car audio installation. It can also occur in professional installs in larger systems or in smaller cars with small batteries and alternators. In order to fix this problem you need to understand why it is happening. Then you can do some basic troubleshooting.


Why Your Headlights Are Dimming


The main reason your headlights are dimming when the bass hits is your alternator does not have enough reserve power to supply the extra demand that your amplifier and subwoofers are creating.
Your stock alternator has reserve power in case your vehicle needs it, somewhere around 30%. And lets say you have a 2002 Honda Accord with a 3.0L motor and a 105 amp alternator. This would mean your alternator should have about 30 amps or so of reserve power. 

If you try to hook up an amplifier that is fused at 60 amps, then guess what, you are asking your vehicles charging system to supply twice as much amperage than it has in reserve. Where do you think that is going to come from?

And because music is dynamic and fluctuates in regards to its need for power, i.e.- bass dropping, your headlights will be dimming every time your subwoofer moves. What I have explained here is the simple explanation. We could go on and on about this, but lets move on to some troubleshooting before you spend any more money.


Troubleshooting Your Headlights Dimming Issue


Your main areas of concern when dealing with this problem are going to be your alternator, your battery, and your grounds. Test your alternator to make sure it is working properly and doesn't need to be replaced due to normal wear and tear. Adding additional load to an old alternator is a common issue because people are so eager to get bass installed that they don't even think about whether or not their charging system is ready for it. 

Then do a battery test when the car is running and when it is off. This way you are sure that it is performing at its best. The worst thing for an alternator is for it to be connected to a weak or low voltage battery.

Also make sure the terminals are clean and their isn't any fluid or leakage that stretches between the positive and negative terminal as this fluid can create a power draw. Your wouldn't believe how many people I have seen connect amplifier power wire to a battery that should have been replaced long ago. 

Next, check your grounds. Especially your amplifier ground. Make sure it is grounded to the chassis. Not to a bolt on a seat or just any metal you can find. It really needs to be chassis grounded. I just can't stress this enough.

Don't try to reinvent the wheel here. Just do it right and don't be lazy. If your ground isn't really good, and by good I mean connected to scraped bare chassis metal, then you aren't grounded at all.


Upgrading Your Electrical Connections


If you have done the aforementioned troubleshooting and your issue still persists then it is time to do some upgrades to your electrical system. Because it is usually the least expensive place to start, I recommend upgrading the size of your wire in your vehicles charging system.

This process includes what is commonly known as the Big 3 (The battery to chassis ground wire, the engine to chassis ground wire, and the alternator to battery positive wire). What size wire you upgrade to depends on the size of your new system.

If doing the Big 3 doesn't help then not to worry, it can't hurt and will be a benefit regardless if you move on to the next fix which is the battery. First make sure you have good battery terminals. They are fairly inexpensive to replace and every once in a while that's all that you need to eliminate the problem.

Then look into getting something like a Stinger battery that is designed to handle the additional accessory loads involved with car audio. If you had already upgraded your battery prior to your problems than look at adding a second battery with an isolator. Upgrading the battery after your wire has solved the headlight dimming issues that I have seen over the last 5 years in the 12 volt industry 9 out of 10 times. 

And finally you will need to upgrade your alternator to gain more amperage. Do not do this before the other steps we have talked about. You can either buy an upgraded high powered alternator, or in some areas there are performance shops that can remove your existing one and have it re spun for more amperage. You should only need to do this step in systems that are 1000 watts or greater. 

It is highly recommended that you consult a professional for any of the work mentioned above. If you have a question feel free to comment below. And don't forget to share or +1 this post!


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