Wires
FIGURE 36-54
Common types of wire.

Electrical wires are used to conduct current around the vehicle Figure 36-54. Wire can also be referred to as cable, although cable typically refers to large-diameter wire. Automotive wire is commonly a multistranded copper core wrapped with seamless plastic insulation. Copper is typically used as it offers low electrical resistance and remains flexible even after years of use. The insulation is designed to protect the wire and prevent leakage of the current flow so that it can get to its intended destination. Ribbon cable is a series of wires that are formed side by side and joined along the wire insulation; they are flat like a ribbon Figure 36-55. Ribbon cable works well when several wires run from one component to another. The ribbon design groups them so they can be routed neatly and easily. Ribbon cable is often found inside computers and other electronic components. It is used for connecting between printed circuits or between printed circuits and other components. Some wires, especially signal wires and communication wires, are shielded, which helps to prevent electromagnetic interference, also referred to as “noise.”

Shielding

In certain locations within a vehicle and in environments where strong electromagnetic interference (EMI) is present, wiring harnesses are subject to a situation where unwanted electromagnetic induction occurs. This interference is referred to as electrical noise or EMI noise. To prevent noise, some vehicles use shielded wiring harnesses. The type of shielding used can be one of three forms: twisted pair, Mylar tape, and drain lines.

Twisted Pair

Twisted pair uses two wires delivering signals to a common component. The wires are uniformly twisted through the entire length of the harness and end at a terminating resistor. The twisted wires along with the terminating resistor have the effect of canceling any noise that occurs in the wires, reducing the loss of data in the transmitted signals. The controlled area network, or CAN , bus in a modern vehicle may use one or more twisted pairs to connect all the vehicle control units with common data line(s) to share information.

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FIGURE 36-55
Wire. A. Standard wire (stripped). B. Ribbon cable (stripped).
Mylar Tape

Mylar tape is an electrically conductive material that is wrapped around a wiring harness inside the outer harness layer. Any noise that attempts to reach the wires inside the shield are absorbed by the Mylar, where it will be conducted to ground via a ground connection. The shielding is important to prevent electrical noise penetrating into the electrical wiring. If the harness is exposed, the Mylar will have to be rewrapped so that noise cannot penetrate into the harness.

Drain Lines

A drain line is a noninsulated wire that is wrapped within a wiring harness. The drain wire is connected to ground at the harness source end and conducts any noise to ground, negating the noise effect. If the drain wire is cut, it will be inoperative, so it is important that the wire not be cut or left disconnected.