Capacitors are used in high-power car stereo installations, when one or multiple amplifiers demand more power than the car's battery can supply. The capacitor stores power during low power consumption and makes it available when more power is needed. Using two amplifiers in an installation will usually require a capacitor.
Connect RCA audio cables to the pre-amp/subwoofer out ports on the deck/head unit of the vehicle. Run the audio cables to the amplifier and plug them into the amp's audio in port.
Connect the speakers to the amplifier. Connect one speaker wire to the "+" speaker out terminal on the amp and connect another speaker wire to the "-" terminal on the amp. Connect both of these wires to the "+" and "-" power terminals on the subwoofers. Always maintain these connections, keeping positive with positive and negative with negative. Repeat this process for all additional speakers.
Connect two power wires to both amplifiers' positive 12 volt power terminals, one wire for each amp. Use the gauge of wire recommended by the manufacturer. Connect these power wires to the positive terminal on the capacitor. Connect two additional power wires to the negative/ground power terminals on the amplifier. Connect each of these terminals to a ground connection, such as the body of the car.
Connect two power wires to the capacitor. Again, use the gauge of wire recommended by the manufacturer. Connect one wire to the positive terminal and connect another to the negative terminal. Run these wires to the car's battery, noting which wire is positive and which is negative. Connect the negative wire to the negative terminal on the battery and connect the positive wire to the positive terminal on the battery.
Start the car and drive around for 10-15 minutes with the stereo on at the lowest volume possible. This will charge up the capacitor. Once the capacitor is charged, test the stereo by turning up the volume.
