Schematic Rise

Parallel wiring involves wiring each speaker positive terminal to the positive speaker output of the amplifier and likewise the negative speaker terminals are wired to the negative speaker output of the amplifier.

Series
Series wiring involves connecting the amplifiers positive terminal to the positive terminal of the first speaker and then connecting the negative terminal of the first speaker to the positive terminal of the second speaker and so on. The final speaker in the chain will have its negative terminal connected to the negative terminal of the amplifier. See the figure below. This wiring scheme is best reserved for multiple subwoofers because any audio artifacts (distortion, frequency attenuation, etc.) caused by the first speaker(s) in the chain will affect the speakers in the chain after it. This is a major problem when mixing multiple speaker types (i.e. woofers with tweeters).

There is often a lot of confusion on how to wire a car audio capacitor (a.k.a. power capacitor or stiffening capacitor). There are two terminals on a car audio capacitor. A positive and a negative. The negative terminal is connected to ground. The positive terminal is connected "in-line" with the car audio amplifier +12 volts terminal. See the diagram below.

Ideally the power capacitor should be as close as possible to the amplifier. Within a couple of feet is acceptable.

Heres how to wire two capacitors in a system:

NOTE OF CAUTION: Power capacitors store a large amount of energy and they charge very quickly. You must first "charge" your power capacitor using a resistor before connecting it directly to +12 volts. This is done with the a 1k ohm resistor and a voltmeter. The exact value of the resistor is not critical but I would keep it in the 500-1k ohm range. I would recommend getting a 1 watt resistor if possible (your capacitor may have come with a resistor for charging). A lower wattage resistor will heat up too quickly. Also, do not hold the resistor with your bare hand. The current flowing through the resistor will cause the resistor to heat up and you could be burned. A good place to put the resistor is in the main power wire fuse holder. Simply substitute the resistor for the fuse. A diagram for the capacitor charging setup is shown below. You will need to place a voltmeter across the capacitor to monitor the voltage. Once the voltmeter reads 12 volts you can remove the voltmeter and replace the resistor with the power fuse.