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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.
WIRE TYPES AND MATERIALS 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
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
