Consider amperage of the audio system you want for your car. Measuring wattage is also necessary before you make the purchase. You can discuss it with the shopkeeper while choosing the components. Wattage is measured by channels you want to tune in on your audio system in the car.
Consider Your Budget
Another important aspect of buying the equipment is consideration of budget. If you want to source quality components, you should have sufficient money, as buying branded and quality products is a costly process.
Visit Local Auto Accessory Store
After consideration of the initial two steps you should visit local auto accessories shops. It is likely you can buy all required components locally, without much hassle. You can also save money on shipping of products if you are buying online.
There are many online stores selling car stereo system. You can buy products that you want or which are compatible to your car's audio system and get them shipped at your address. It is likely you get some discount as components being sold online are comparatively cheaper to those available at shops' counters.
Get It Installed Directly From Car Stereos Stores
You can also get the amplifier installed from cars stereo stores, especially if you do not know how to do it. This way you can also save some money on the installation and there is a fair chance you can negotiate their price at the store. If they do not have right equipment available for you at the time you visit the shop, you can order it and they can source it for you from their suppliers.