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Electrical Diagrams and Wiring
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
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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.
Wire Gauge Number
Figure 6-6. Automotive wiring may be solid-wire conductors or multistrand-wire conductors. (DaimlerChrysler Corporation)
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
Figure 6-8. This table lists the most common wire gauge sizes used in automotive electrical systems.
Corporation)
(DaimlerChrysler Corporation)
