How to Hook Up Subwoofer Power Cables in a Car

Written by pauline gill
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How to Hook Up Subwoofer Power Cables in a Car
Car stereo woofers require hundreds of watts of clean power. (speaker stack image by Nicemonkey from

Subwoofer power cables are the substantial direct current (DC) power conductors between a vehicle's 12-volt battery and the large audio amplifier that drives the subwoofer speakers. The subwoofer amplifier receives dedicated subwoofer frequencies from the vehicle's sound system and sends hundreds of watts into the large speakers to reproduce these powerful sounds. The nominal 12-volt DC system therefore requires a hookup strategy that can supply large amounts of direct current efficiently under all operating conditions.

Skill level:

Things you need

  • Power cabling, 10 gauge
  • Power capacitor
  • Electrical tools
  • Workshop tools
  • Cable terminals
  • Power fuse, 30-amp size
  • Power relay

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  1. 1

    Route the cables from the subwoofer amplifier to the vehicle's battery. Subwoofer amplifiers are usually mounted in the boot right next to or right on the subwoofer itself in the case of a powered subwoofer. Pass the cabling under the driver's seat. Cut only the positive cable under the driver's seat and install a 40-amp master power switch between the two cut ends. This switch allows the driver to immediately cut power to the subwoofer system if necessary.

    How to Hook Up Subwoofer Power Cables in a Car
    Automotive speakers deliver strong sound even over road noise. (car audio speakers image by Alexander Zhiltsov from
  2. 2

    Install the power capacitor in the boot right next to the subwoofer amplifier. The capacitor size should be at least 1 farad per 1000-watts of amplifier rating with a 1-farad minimum size. Connect the designated positive power cable to the capacitor's positive terminal (red) and to the amplifier's power positive input (red). Connect the designated negative power cable to the capacitor's negative terminal (black) and to the amplifier's power common or ground input (black).

  3. 3

    Mount the 30-ampere fuse as near to the vehicle battery's positive post as possible. Connect the fuse in series between the designated power positive cable for the amplifier and the battery's positive terminal. Make sure the master switch under the drivers seat is off. Then connect the designated negative cable end to the battery's negative terminal.

  4. 4

    Secure the cable along its entire route with cable ties if necessary. Check that the cable does not cross sharp edges along any part of its length. Also make sure that any holes through the firewall are sealed with high-temperature RTV silicone sealant both inside and out.

  5. 5

    Route a wire between the car stereo head unit's remote-on lead to the subwoofer amplifier's remote-on input connector. Do this installation at the same time the subwoofer audio input cable is being routed to the amplifier in the boot. The remote-on signal will automatically turn the subwoofer amplifier on-and-off to correspond with the car stereo system head unit.

  6. 6

    Keep the master switch under the driver's seat off. Turn on the car stereo and select program material with powerful bass or use a system test compact audio disc. Turn the subwoofer's volume to a low (30-percent) setting and turn on the master switch. You should hear a difference between the subwoofer system on and off. Increase the subwoofer volume against the car stereo's volume until the low bass is balanced against the stereo program.

  7. 7

    Check the power capacitor's digital display and compare it to the messages in the owner's manual. If it reads vehicle voltage, the capacitor is working correctly. The capacitor keeps a massive local storage of electrical current on-hand and available to the subwoofer amplifier for huge sub-bass impact sounds without draining the car's instantaneous electrical capacity (such as dimming the vehicle's lights momentarily while driving).

Tips and warnings

  • Always use a capacitor with separate subwoofer or even regular stereo channel amps to bolster the system's available amplification capability.
  • Run a dedicated ground cable between the capacitor and amplifier ground or negative connection and the vehicle battery's negative terminal.
  • Periodically check the capacitor's readings to assure correct operation.
  • Never connect an audio component directly to the battery of a vehicle without a completely separate switch and fuse close to the battery.

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