Introduction
Car electrical systems are powered from a 12-Volt DC
battery located in the engine compartment. This battery has
two terminals to which electrical components are connected.
The first is the positive, which is marked by a + sign and
is usually colour coded as red. The second is the negative,
which is usually marked as - and is colour coded to be
black.
Many components throughout the car will be connected to
the positive terminal of the battery. However, most of
these will not connect directly to the negative terminal.
Instead, the negative power leads of most devices are
instead "grounded". Grounding a cable is done by attaching
one end of the cable to something metal in the car that is
connected, either directly or through other metal
components, to the chassis. The chassie in turn is
connected to the negative terminal of the battery, often via
the engine.
Electrical systems throughout cars are powered in this
manner. Power flows through cables from the positive
terminal to where its needed, and the circuit back to the
battery is then completed via a cable from each device that
ultimately connects to the chassie.
Almost all systems, particularly those used for car
audio, will be supplied with 12 volts. These systems will
then draw differing amounts of current, measured in amps,
depending on how much power they need. For example, a 200
watt amplifier will in theory draw 16.6 amps. That's
because 16.6 amps multiplied by 12 volts is equal to 200
watts.
Speaker Wiring
Speakers come in many different shapes and sizes for
producing many different types of sound. However, just like
with electrical wiring, all speakers are connected by two
wires, one positive and one negative. But that is where the
similarity ends. Unlike electrical wiring, the negative
terminal of an audio cable needs to be connected all the way
back to the source that is producing the sound.
Speakers are usually connected specifically with speaker
cable. This is easily recognisable by the fact that it has
two separate wires that are attached side by side by their
outer coating. There is no set colour for speaker wire.
Usually, both wires will be the same colour, but one will
have a line, often black, running all the way along
the wire. The wire with the black line is by convention,
used as the negative wire, although this makes no actual
difference to the connection.
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