Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

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92 Chapter Six
trucks also are considered low-voltage systems.)
The low-voltage wiring of a vehicle, with the
exception of the battery cables, is called the
primary wiring. This usually includes all lighting,
accessory, and power distribution circuits. By 2003,
we will see 42-volt systems in some hybrid and
mybrid applications. For more information about
diagnosing wiring problems, see the “Tracing
Circuits” section in Chapter 6 of the Shop Manual.
Figure 6-4. The engine compartment wiring harnesses.
(GM Service and Parts Operations)
Figure 6-5. The engine wiring harnesses connects to
the individual engine components to the engine compartment
wiring harness. (GM Service and Parts Operations)
these harnesses, especially where sections of the
wire are hidden from view.
Aloose or corroded connection, or a replacement
wire that is too small for the circuit, will add extra
resistance and an additional voltage drop to the circuit.
For example, a 10-percent extra drop in voltage
to the headlamps will cause a 30-percent
voltage loss in candlepower. The same 10-percent
voltage loss at the power windows or windshield
wiper motor can reduce, or even stop, motor operation.
All automotive electrical circuits, except the
secondary circuit of the ignition system (from
the coil to the spark plugs), operate on 12 to 14 volts
and are called low-voltage systems. (Six-volt
systems on older cars and 24-volt systems on
WIRE TYPES AND
MATERIALS
Most automotive wiring consists of a conductor
covered with an insulator. Copper is the most common
conductor used. It has excellent conductivity,
is flexible enough to be bent easily, solders readily,
and is relatively inexpensive. A conductor must be
surrounded with some form of protective covering
to prevent it from contacting other conductors.
This covering is called insulation. High-resistance
plastic compounds have replaced the cloth or paper
insulation used on older wiring installations.
Stainless steel is used in some heavy wiring,
such as battery cables and some ignition cables.
Some General Motors cars use aluminum wiring in
the main body harness. Although less expensive,
aluminum is also less conductive and less flexible.
For these reasons, aluminum wires must be larger
than comparable copper wires and they generally
are used in the lower forward part of the vehicle
where flexing is not a problem. Brown plastic wrapping
indicates aluminum wiring in GM cars; copper
wiring harnesses in the cars have a black wrapping.
Wire Types
Automotive wiring or circuit conductors are used
in one of three forms, as follows:
• Solid wires (single-strand)
• Stranded wires (multistrand)
• Printed circuitry
Solid or single-strand wire is used where current
is low and flexibility is not required. In automotive
electrical systems, it is used inside
components such as alternators, motors, relays,
and other devices with only a thin coat of enamel
or shellac for insulation. Stranded or multistrand