How to Wire an Amp & Subwoofers Into a Stock Stereo

By Kevin Krause

Stock car stereo systems usually do not pack much punch. To really highlight the bass of your car stereo, you need a setup capable of properly reproducing low frequency notes. Adding a subwoofer and amplifier to your existing stereo is a great way to improve the bottom-end output of your system and is one of the most common upgrades performed on a car's audio gear.

Step 1

Choose a subwoofer speaker system and amplifier that fits your car's current system and meets your audio needs. You have two basic options: You can purchase a separate amplifier and speaker or you can purchase a powered subwoofer with a built-in amplifier. When purchasing either form of amplification, look for an amp that accepts high-level signals. This allows you to run a high level speaker signal from your stock stereo's powered head unit without any additional wiring. If you purchase an amp without speaker level inputs, you will need to also purchase a line-out converter to alter the output of your stock head unit to a low-level signal to be accepted into standard speaker connections on your amp.

Step 2

Position your amp and speaker in your car. Subwoofers can be large speakers that are usually housed in speaker enclosures installed in the trunk of the car. Your amp could be installed near the speaker in the trunk or under a seat. Mounting brackets and speaker enclosures can be purchased at any local car audio retailer.

Step 3

Connect your amplifier or powered sub to your car's stock head unit. If your amp accepts high level signals directly, simply match the appropriate speaker output wires from your head unit to the appropriate speaker level inputs on your amplifier. If your amplifier accepts line level signals only, you will need to cut the wires coming from the back of your head unit and splice them to the corresponding wires on a line-out converter. This converter can then be connected directly to your amplifier's line level inputs. Check the manuals included with your line-out converter, stereo and amplifier for complete installation instructions for your system.

Step 4

Connect your amplifier to your speaker by running the positive and negative speaker wires to the proper terminals on your speaker. Most amplifiers will have outputs for at least two speakers. You could add additional subs to your system using these outputs. Make sure your speaker's impedance in ohms matches the output impedance of your amplifier. If you installed a powered sub, you will not need to connect the amplifier and speaker, as they are already connected.

Step 5

Connect the amplifier's +12 volt power cable to the electrical system of your vehicle. Connect the ground from the amplifier to the chassis.

Power on your car and stereo system and test your subwoofer for output. If the sound is scratchy, check that your connections are secure. If all connections seem correct but the speaker is not functioning properly, consult an expert at your local electronics store.