How to Add an Amplifier to a Factory Stereo

By Joseph Eitel

Sony Amplifier
i Sony

It's possible to add an amp to your car's factory audio system without having to buy an expensive new head unit (CD player). Adding an amp will make your audio system sound louder and clearer by allowing you to send more power to your factory speakers or sub-woofers. This tutorial will focus on how to add an amp by using speaker-level inputs to tap into your car's existing wiring. The installation is quick and easy and won't require removing your factory head unit.

If you don't already have one, purchase a car amplifier with speaker-level inputs and also purchase an amp installation kit. These inputs look like regular speaker wire inputs and they will be labeled "speaker-level inputs" or something very similar.

Disconnect your car battery's negative terminal for safety purposes.

Run the red power wire (from your amp installation kit) from the positive terminal on your battery through your car's cabin to the location of the amp. The best location for the amp is usually the trunk. You can mount the amp on a sidewall, on the rear of the back seats or on the floor by using regular 1/2-inch screws to secure it firmly in place. Every amp has pre-drilled mounting screw holes located on each of the four corners of the amp for easier mounting.

Connect your ground wire (from your amp installation kit) to a nut/bolt located on your car's chassis near the location of the amp. You can usually find one on the sidewall behind the carpeting. Make sure to scrape off any visible paint so that the ground wire is in full contact with the metal of your car's chassis, otherwise the amp will not function properly.

Speaker-level inputs and speaker outputs

Locate your car's rear speakers -- specifically the factory speaker wires running to these speakers. Carefully splice into the positive and negative wire on both the right and left rear speakers using a wire stripper. Now attach a line of speaker wire to each splice and secure with electrical tape. Run this wire back to your amp and hook it into the speaker-level inputs. Make sure to put the right rear positive wire into the right rear positive speaker-level input, and do the same for right rear negative wire until all four of the wires are connected.

Now that your amp is tapped into your car's factory audio system, run speaker wires from the amp's speaker outputs to the speaker(s) or sub-woofer(s) you want the amp to power. Make sure to connect positive to positive and negative to negative.

Connect the red power wire and ground wire you prepped earlier to the proper inputs on your amp. Secure all of the amp's connections tightly using a screwdriver.

Reconnect your car battery, and test your new audio system. If the amp doesn't seem to be working properly, disconnect your battery again and go back and double-check all of your wiring for possible damaged wire, grounded wire or loose connections.