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

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Electrical Diagrams and Wiring 93
wire is made by braiding or twisting a number of
solid wires together into a single conductor insulated
with a covering of colored plastic, as shown
in Figure 6-6. Most automotive electrical system
wiring uses stranded wire, either as single conductors
or grouped together in harnesses or
looms. For more information about wire types,
see the section on “Copper Wiring Repair” in
Chapter 6 of the Shop Manual.
Printed circuitry is a thin film of copper or
other conductor that has been etched or embedded
on a flat insulating plate (Figure 6-7). A complete
printed circuit consists of conductors, insulating
material, and connectors for lamps and other
components, and is called a printed circuit (PC)
board. It is used in places where space for individual
wires or harnesses is limited, such as
behind instrument panels.
WIRE SIZE
Automotive electrical systems are very sensitive
to changes in resistance. This makes the selection
of properly sized wires critical whenever systems
are designed or circuits repaired. There are two
important factors to consider: wire gauge number
and wire length.
Figure 6-6. Automotive wiring may be solid-wire conductors
or multistrand-wire conductors. (DaimlerChrysler
Corporation)
Wire Gauge Number
A wire gauge number is an expression of the
cross-sectional area of the conductor. The most
common system for expressing wire size is the
American Wire Gauge (AWG) system. Figure 6-8
is a table of AWG wire sizes commonly used in
automotive systems. Wire cross-sectional area is
measured in circular mils; a mil is one-thousandth
of an inch (0.001), and a circular mil is the area of a
circle 1 mil (0.001) in diameter. A circular mil measurement
is obtained by squaring the diameter of a
conductor measured in mils. For example, a conductor
1/4 inch in diameter is 0.250 inch, or 250 mils, in
diameter. The circular mil cross-sectional area of the
wire is 250 squared, or 62,500 circular mils.
Figure 6-7. Printed circuit boards are used in automotive
instrument panels and elsewhere. (DaimlerChrysler
Corporation)
Figure 6-8. This table lists the most common wire
gauge sizes used in automotive electrical systems.
(DaimlerChrysler Corporation)