How to Wire a New Car Stereo in an Old Car

Written by martin wolfson
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Wiring can dramatically impact your car stereo performance. Professional installers know that wiring can make the difference between manufacturers' quality and superb, state-of-the-art car audio ability. When wiring a new car stereo in an old car, this likely means that the vehicle does not use a wire harness. Use crimp connectors rather than solder to interconnect the wires from the in-dash head unit to the speakers and amp. Use wire strippers to bare the ends of the cables. Run power cables and speaker cables down separate paths in the car to minimise signal interference and distortion.

Skill level:

Things you need

  • Guide to removing the dash and speaker panels of your car
  • Pliers
  • Utility knife
  • Wire cutters
  • Screwdrivers
  • Wire strippers
  • Amplifier wiring kit
  • Electrical tape

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  1. 1

    Run separate wires for each speaker in your vehicle. This will always include front doors, and may include seat backs, rear doors and/or rear decks for a subwoofer.

  2. 2

    Run extra wire while doing the installation. Wire is very economical, and it's better and easier to run wire for a future component--that is, a rear subwoofer--even if it's not to be installed at the same time. Use 14-gauge speaker wire for all connections.

  3. 3

    Run amplifier cable from its installation point (often under a seat) to the head unit in the dash. Always leave a good 10 inches of extra cable or wire length to enable easy removal or swapping out of components.

  4. 4

    Crimp the connections to the wires coming out of the head unit. Crimping is faster, less messy, and more easily undone than soldering the wires. It also allows for replacing the new in-dash unit with the original when selling the car.

  5. 5

    Connect each appropriate head unit wire individually to its corresponding wire in the dash. The wires are colour coated for convenience. Crimping different gauge wires is fine.

  6. 6

    Make power wires and speaker wires as separate as possible. Install them in separate paths in the car or truck. If they must cross, cross as close to perpendicular as possible, and cross only once. Cables from the amp can induce hum in speaker wires.

Tips and warnings

  • Have the car service manual at hand.
  • Check speaker polarity with a 9-volt battery. If wires are not colour coded, use the battery to determine positive and negative. If the speaker moves forward or out, the positive lead of the speaker is connected to the positive terminal of the battery. If the speaker moves back or in, then the wire touching the positive terminal of the battery is the negative speaker wire, and the speaker is potentially out of phase. Reverse the wires in this case.
  • Always disconnect the ground cable (negative lead) from your car battery first. NEVER work on the electrical system of a vehicle without disconnecting the battery lead.

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