To install an external power amplifier to a car audio head unit, you will need to use a line-level or low-level signal converter if the head unit doesn't have a line-level output. A line-level output is the two audio connections, usually with one colored red and the other colored white, that you plug RCA audio cables into to transfer the audio signal from one piece of equipment to another. If your head unit only uses speaker outputs, you will need to use a adjustable line-level converter to connect your amplifiers.
Instructions
1. Remove the head unit. There are several different head units and factory decks on the market, so consult your deck's owners manual for proper removal instructions.
2. Locate the wire harness coming from the back of the deck. Consult the deck's owners manual to find the speaker wires for the left and right front and remove about an inch of the jacket on both wires with your wire strippers.
3. Connect the end of the right-channel wire from the line-level controller to the bare wire you just exposed on the wire harness. Wrap the bare wire from the converter around the exposed wire from the harness, then secure the two wires together using electrical tape. Repeat the process for the left-channel wires.
4. Plug the RCA cable into the line-level controller's audio output. Insert the red plug into the right-channel output on the converter and the white plug into the left-channel output.
5. Connect the other end of the RCA cable into your amplifier's input.
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