Most cars, especially those made ten or more years ago, have rudimentary and often unappealing sound systems. For some drivers it is not important, but others need quality entertainment for the road. Some drivers just need to upgrade the head unit to play the media they want in a practical way, while others prefer to increase the clarity and sound of their music with additional amplifiers and speakers. Either method is fine, as long as it meets your needs. With a little time and money, you can turn your car into a mobile entertainment center.
Steps
Method 1 of 3: Update the main unit

Step 1. Select a new head unit
There are many brands and options available. Kenwood, Pioneer, JL audio, and Sony are the best in this category. Each of these brands offers a full line of sound equipment to suit different needs and budgets.

Step 2. Purchase cable sets for the main unit and the vehicle
Match the colors in the games or follow the included diagram. This makes it much easier to install and then remove the head unit if you decide to take it to another car, and a harness adapter usually only costs around $ 20 or less.
You may also need to purchase an antenna adapter for the new head unit and vehicle

Step 3. Purchase a service manual for the car
You will need a service manual like Haynes, but any manual that provides details for your make and model should work. Every stereo is different, and sometimes you need to remove parts of the dash or console to remove the stereo. This is where the manual will be most useful. It can also be helpful to have a comprehensive guide on installing the replacement stereo.

Step 4. Unhook the battery ground terminal
This will cut power to the car and allow you to safely work on electrical components (such as the stereo wiring).

Step 5. Remove the original main unit
Typically this will consist of removing a portion of the dash or faceplate (see your service manual) and then removing the mounting screws holding the main unit. Once you do, the unit will slide out.

Step 6. Unplug the wiring harness
It will connect to the back of the main unit. You will have access when you remove the main unit.
Some people choose to cut these wires (especially if they didn't buy a wiring adapter) but doing so can void the warranty

Step 7. Connect the harness adapter to the new head unit
The cables will be clearly marked, as the adapter is designed so that the car and the head unit fit together. Crimp the cables as instructed in the instructions for the cable set adapter. After crimping (or soldering as some choose to do), twist the wire nuts to the appropriate size and make sure to keep the wires as clean as possible.

Step 8. Connect the harness adapter to the factory harness
This part is even easier than connecting the adapter to the main unit. It is literally designed to connect directly to the factory wiring harness. Do it now.

Step 9. Connect the main unit to the antenna
If you need an antenna adapter, you can plug it into the back of the main unit and connect the antenna cable to the adapter. Otherwise, the antenna must be connected directly to the back of the main unit.

Step 10. Mount the new main unit
The size of your original and replacement head units may be different. They generally come in one of three sizes: Single DIN, Half DIN, Double DIN. If your replacement main unit is a different size than the original, you may need a DIN adapter or battery holder to mount it.
If they are the same size, the replacement stereo must be screwed into the original mounting brackets for the main unit

Step 11. Replace the dash components
This is where the service manual will come in handy again. Now you need to reassemble the dash pieces that were removed to remove the stereo.

Step 12. Reconnect the battery ground terminal
This will restore power to the car and thus the new head unit.

Step 13. Test the stereo
Now you should be able to turn on the stereo and enjoy crisp, clean sound.
Method 2 of 3: Upgrade by Installing an Amplifier

Step 1. Match the amplifier (amp) to the system speaker load
Amplifiers have a designated power and impedance rating. This rating should match the load you put on the amp. A low quality or low power amplifier combined with tall speakers will not take full advantage of the quality of the speakers. An amp that is too powerful will blow your speakers up in a couple of months.

Step 2. Remove power from the car's electrical system
This can be done by disconnecting the ground wire from the battery. Doing so will prevent injury or damage to the vehicle while working with the wiring inside the car.

Step 3. Find a place for your amp
This is important to do things well. You need the amp to be somewhere where it can safely disperse heat. Otherwise, it will burn and may start a fire. If you have an open space in the trunk it is usually ideal. Sometimes another alternative is to place the amplifier under or behind the seats, but make sure there is enough room for it to ventilate.

Step 4. Connect the amplifier to the main unit
The use of RCA cables is recommended to connect the amplifier to the main unit, as they isolate the cable and dampen any signal distortion. It is also recommended that the cables be routed to the side of the car opposite the amplifier power cable to avoid signal interruptions that negatively affect the sound quality.

Step 5. Power up the amp
The amplifier must be connected to a switching power supply. In this way, there is only power when the car is on. The power cord (also known as the remote start cord) is sometimes connected directly to the main unit. Otherwise, you will need to connect it to a switching power source, such as the main unit power supply or the power switch.

Step 6. Ground the amplifier
You'll need to connect the amplifier's ground wire to another ground wire or to any grounding point on the car. Grounding points are bare metal surfaces (clean, unpainted). Make sure to do it somewhere where no one accidentally touches it.

Step 7. Connect the positive terminal of the amplifier to your speakers
The purpose of the amplifier is, after all, to amplify the signal coming from the main unit to fully utilize the speakers. You may need to cut the speaker wires from a spool of wire and strip enough insulation from the end to fit the amplifier terminals. Each wire should go to its corresponding speaker and connect to the positive terminal of the speaker.

Step 8. Connect the negative terminal of the amplifier to the speakers
For all series-connected speakers, connect only the negative wire from the last speaker to the negative terminal on the amplifier. For all speakers connected in parallel, connect the negative cable from each speaker to the negative terminal on the amplifier.
Method 3 of 3: Update the speakers

Step 1. Match the speakers to the amplifier
The amplifier has a specific power and impedance. The speaker load must meet these ratings. Otherwise you will blow them up or burn out the amp. You should understand the basics of speaker wiring before starting the job.

Step 2. Buy the best quality speakers in your budget
No matter how much you spend on an amp or head unit, if you have low-quality speakers, you'll get equal quality sound. Speakers range from 2.5-centimeter (1-inch) tweeters to 37.5-centimeter (15-inch) or larger bass drivers. In general, a smaller speaker provides clearer highs and larger speakers produce deeper bass. Midrange speakers come in 2-way (play high and low) and 3-way (play mid high and low).

Step 3. Find a place for the speakers
Speaker placement is important to consider. The difference in distance between the listener and a speaker compared to the others will change the perceived sound. It is recommended that the speakers go into the fender panel when possible. However, it is sometimes necessary to place them elsewhere, such as in the trunk, for space purposes.

Step 4. Connect the speakers to the amplifier
As described in the "Upgrading by Installing an Amplifier" section, you will need a spool of cable to go from the speakers to the amplifier (unless you replace an existing speaker and the cable is already there). The wiring will be different depending on whether you install the cables in series or in parallel.
Advice
- If you seem to be having trouble with the car's electrical components after updating the sound system, consider installing a capacitor or updating the battery or alternator.
- The size of the cable depends on the quality of the wiring used, the type of conductor and the number of wires. Many audio companies manufacture high-quality cabling equipment specifically for amplifier installations.
Warnings
- Grounding is possibly the most critical connection in the installation. Make sure to properly clamp the ground wire and use bare metal.
- On the head unit, turn down the volume before turning off the car so as not to damage the speakers and your eardrums when you turn it on.
- Make sure to use properly insulated and calibrated wiring for the amplifiers. Consult AWG's wiring standards guide to find out what gauge wire should be used for your application. Using a smaller cord than necessary can cause an electrical fire.
- Ground the amplifier and fuse the power cord. The fuse should never be more than 30 centimeters (12 inches) from the battery. You should ALWAYS use the same gauge ground wire as the power cord. Never use cables of different sizes.