1. Check Power Contacts, Grounds and the Battery

The electrical system needs solid contact to transfer power as efficiently as possible. Contacts that have grown dirty or crusted will have a higher resistance to power transfer, which means other parts of the system suffer. The first step is to check each of the power and ground connections. Make sure these are scraped and cleaned to bare metal, and that nothing obstructs the flow of power.

If this does not solve the problem, the battery itself may be the issue. Take the battery to an auto parts store to have it load tested. This is typically a free procedure, and if the battery is damaged or faulty, a new one can be purchased and installed easily. Batteries & power cells have an average life span of four years. Older batteries may be able to run the car without issue, but falter when a high-powered audio system kicks in.
2. Add a Capacitor

Capacitors are devices that help regulate an electrical system. When voltage is too high, the extra power is stored in the capacitor. When voltage drops, the capacitor discharges that stored power in order to keep the current flowing.

A capacitor will not solve headlight-dimming issues if they are constant and major. However, if the headlight dims only rarely, and only when the amps are kicked into high gear, it could mean that they draw too much power too quickly for the system to handle.

For these minor power fluctuations, a capacitor is an ideal way to regulate the flow of power from the battery and alternator to the stereo system. Capacitors are measured in farads, which is a unit of capacitance. Two farads of capacitance for every thousand watts in the stereo system is an ideal level. It is actually higher than the typical recommendation, but it will allow the capacitor to recharge quickly and keep power flowing evenly.
3. Perform the Big Three Wiring Upgrade

There are three primary and important cables in the electrical system of a car with an auxiliary audio system. These “big three” cables, when upgraded, will vastly increase the capacity of the electrical system. This means that if the headlights are dimming because not enough power can flow to them through the system, they will now have plenty of juice to run. On the other hand, if the cause of dimming headlights is the power consumption and not a restricted power flow, this upgrade will cause the problem to worsen. This is because the audio system will be able to draw even more power, causing the headlights to receive even less.

The three cables that need to be upgraded are the alternator plus to battery plus cable, the chassis to engine block cable and the battery ground to chassis cable. Each of these cables can be replaced with either 1/0 gauge or 4 gauge wire in order to increase their carrying capacity.

In the event that this upgrade causes the problem to worsen, there is no need to revert to older wires. It is still a valuable upgrade in any case, and other solutions on this list will still solve the problem.
4. Install a Higher Output Alternator

The alternator is the source of all power when the car is running. The battery is necessary in order for the vehicle to start, but once it is running, all power usage comes from the alternator. If none of the steps above have helped the headlight-dimming problem, it is possible that the stock alternator simply does not put out enough power to feed everything in the electrical system. Headlights are easy to see, but every part of the electrical system will suffer from insufficient current.

Unfortunately, a high output alternator is an expensive solution. That said, it is a worthwhile investment for many vehicles and will last for quite a long time. For a 1500-watt sound system, the alternator needs to be able to produce around 220 amperes of current. Most alternators are designed with the standard vehicle hardware in mind, and will produce no more than 120 amperes of current. Music does not use the full 220 amperes the majority of the time, and only when it tries to draw that much power will the electrical system suffer. For such a sound system, an aftermarket alternator that produces around 300 amperes will be sufficient.

5. Install a Second Battery

Adding a second battery to a car with an aftermarket sound system is a good idea, especially of none of the other solutions above work and an alternator is out of the price range. A second battery is typically installed in the rear of the vehicle, near the sound system’s amp.

It is a good idea to isolate the batteries from one another. This way the primary battery is never drained when playing music, so the car never has issues starting. It is also a good idea to use two batteries with the same strength and of the same age. Using one new battery and one old battery leads to imbalances in power. The batteries will equalize these differences, but the constant change between them will shorten their life spans.

For a vehicle used to play music with the engine off, a second battery is virtually required. Without the engine running, the alternator does not provide power, and so the sound system is powered entirely by the car battery. This can lead to the battery draining and the car needing a jump-start.

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