Electrical Components CHAPTER Electrical Components 4 Instructor Name: (Your Name)

Learning Objectives Describe the components that make up a truck wiring harness Repair a damaged section of wire Determine the correct wire gauge to be used based on the amperage and length of the conductor Describe the different types of electrical switches using terms such as poles, throws, normally open, and momentary contact

Learning Objectives (continued) Use a voltmeter to determine if a switch is open, closed, or defective Define the function of each terminal of a standard ISO relay Troubleshoot a circuit controlled by a relay and list the most likely failures of a relay Explain how circuit protection devices (CPD’s) operate and the importance of replacing a CPD with the rating specified by the OEM

Learning Objectives (continued) Use a voltmeter to determine if a CPD is open Locate an open circuit and shorted to ground circuit, using wiring schematics and electric test tools

Wiring Harnesses A wiring harness is a modularized section of wires designed to be connected to electrical components and other wiring harnesses Connectors are interlocking devices that permit connections to electrical components or wiring harnesses Terminals are electrically conductive pins (male) and sockets (female) that provide electrical connections between two connectors

Typical Wiring Harness Figure 4-1 Typical wiring harness.

Tech Tip You may find that one or more terminals may be missing in a multi-terminal connector that has been exposed to road salt mixed with water, while the other terminal may only have a small amount of corrosion. Terminal in the connectors supplied with constant battery power can dissolve in a brief amount of time when exposed to salt water.

Wire Details Stranded wire, wire made up of several smaller-diameter wires, is the most common found in use in trucks Wire diameter is most commonly measured by the American Wire Gauge (AWG) or International Organization Standardization (ISO) Wire size is the actual conductor not including the insulator

Stranded Wire Figure 4-2 Stranded wire.

Wire Details (continued) The smaller the AWG number gets the larger the wire diameter gets Cable is often used to describe large-diameter wires ISO metric wiring indicates the cross- sectional area of the wire in mm² The larger the ISO rating the larger the wire diameter

AWG and ISO Wire Sizes Figure 4-3 AWG and metric ISO wire sizes.

Wire Details (continued) The resistance of a wire decreases as the diameter increases The resistance of a wire increases as the length of the wire increases Because resistance increases with length, it may be necessary to increase the wire gauge for loads that are a long distance for the voltage source Automobiles often use polyvinyl chloride material as an insulator Most insulators are color coded to provide circuit identification on the vehicle

Chassis Ground Current needs a path from the positive terminal of the battery through electrical device and back to the negative terminal of the battery The negative terminal of the battery is connected to the steel frame rails providing the return path When the negative battery terminal is connected to the frame rail it is said to have a negative ground With a negative ground system, only a positive wire is needed from the battery

Typical Chassis Ground Symbols Figure 4-6 Chassis or frame ground symbols: a low-resistance circuit is assumed.

Flexible Conduit Protects Wire Insulation from Abrasion Figure 4-7 Flexible conduit protects wire insulation from abrasion.

Wiring Harness Repairing Standard compress or crimp type butt connectors are fast Heat-shrinkable butt connectors are preferable Terminals come in three color coded sizes; red, blue, and yellow Soldering wires, then covering with a heat shrinkable tubing, is the preferred method for repairing if time allows Plastic or electricians tape is not acceptable for sealing wiring repairs outside the cab

Crimp-Type Butt Connectors With Heat-Shrinkable Insulation Figure 4-8 Crimp-type butt connectors with heat-shrinkable insulation.

Connectors and Terminals Molded connectors contain terminals molded in a rubber or soft plastic material. Molded terminals are often designed to mate with a specific device or component. Hard shell connectors contain 1 to 80 terminals. Hard shell connectors are used to provide interconnections between wiring harnesses and electronic control modules.

Sealed Connectors Figure 4-12 Individual wire seals installed before crimping terminals to wire end. Figure 4-11 Hard-shell connector body. Figure 4-13 Multi-wire connector seal.

Crimping Terminals Figure 4-14 Terminal crimping tool. Figure 4-15 Wire end and terminal before and after crimping operation.

Installing Terminals Figure 4-17 Wire with terminal and individual seal is inserted into connector body. Figure 4-19 Pull-to-seat terminals: terminal is crimped to wire end after inserting wire end into connector body and seal.

Installing Terminals (continued) Figure 4-20 Pulling the terminal to seat into place in the connector body after terminal is crimped to wire end. Figure 4-21 Special terminal extracting tools.

Switches When a switch is on it is closed When a switch is off it is open The two pieces of a switch that actually make or break current are known as contacts Poles describe the number of input terminal a switch has Throw describes the number of positions a switch can be moved to and still complete a circuit The terms pole and throw are used together to describe the basic functionality of a switch

Knife Switch Figure 4-22 Knife switch.

Switch Types Figure 4-23 Single-Pole Single-Throw (SPST) Figure 4-24 Double-Pole Single-Throw (DPST) Figure 4-25 Single-Pole Double-Throw (SPDT)

Switches (continued) Latching switches remain in the position they are placed in Momentary contact switches open or close the circuit as long as the user holds the switch The normal state of a momentary switch is the contact position when the switch is not activated NC = normally closed NO = normally open

Figure 4-28 Voltage drop across closed and open switch.

Switch Troubleshooting Figure 4-30 High resistance switch. Figure 4-31 Open circuit before switch. Figure 4-32 Open circuit after switch.

Relay Components Figure 4-33 Relay components.

Terminal Designation and Function of a ISO or DIN Relay 85 and 86 – Coil terminal, normally 50Ω to 100Ω of resistance between them 30 – Common terminal. Normally connected to power source. 87 – Normally open terminal. When the relay is energized the 30 and 87 terminal will close 87A – Normally closed terminal. When the relay is energized the 30 and 87A terminal will open

ISO or DIN Relay Terminals and Footprint Figure 4-34 Common relay terminals and footprint.

Typical Relay Contact Schematics Figure 4-35 Typical relay contact schematics.

Larger Relays Figure 4-38 Components of a magnetic (mag) switch.

Circuit Protection Devices Circuit protection devices (CPD) primary purpose in a truck is to protect the wiring harness CPD’s include fuses, circuit breakers, fusible links, and positive coefficient devices CPD’s allow current flow up to the current rating then melt and open the circuit OEM’s select current rating based on the smallest wire in the circuit being protected

Circuit Protection Devices Any additional wiring added to a truck should be protected by a CPD Never replace a wire with a wire of smaller diameter Some CPD’s are designed to open more slowly or more quickly then others to permit inrush current Common causes for excessive current flow in a circuit are excess current drawing devices or a short to ground Always replace a CPD with the OEM recommended rating

Typical Automotive Fuses Figure 4-41 Blown or Open Fuses Figure 4-42 Automotive Type Fuses

Circuit Breakers Circuit breakers are a form of CPD’s Circuit breakers have thin bi-metal strips that when heated bend or snap and open the circuit An open circuit breaker is considered tripped When the circuit breaker cools it resets There are three SAE classifications of circuit breakers; Type I, II and III

Circuit Breakers (continued) Type I circuit breakers automatically reset after they cool down Type II circuit breakers automatically reset after the cause of the excess current draw is no longer present Type III circuit breakers manually reset after the excess current draw is no longer present and the bimetal strip cools

Type I, II, And III Circuit Breakers Figure 4-48 Type I Figure 4-50 Type III (A) and Type II (B).

Application of Circuit Protection Devices Figure 4-53 Figure 4-54 One fuse protecting several circuits. One fuse for each parallel branch.

Typical Truck CPD Layout Figure 4-55 Typical truck CPD layout.

Terminology for Wiring Problems Open circuit - a circuit with high or infinite circuit resistance, which results in reduced or interrupted current flow in the circuit Short to ground – occurs when the conductor in a circuit has an unwanted contact with ground Short to battery positive - occurs when the conductor in a circuit has an unwanted contact with positive voltage source Wire to wire short – Occurs when the conductor in a circuit has unwanted contact with another wire

Types of Wiring Defects Figure 4-57 Types of wiring defects: (A) Open circuit, (B) short to ground, (C) short to battery positive, (D) wire to wire short.

Basic Electrical / Electronic Diagnostic Procedure Flowchart Figure 4-48 Diagnostic flowchart.

Common Wiring Diagram Schematic Symbols Figure 4-59 Common wiring diagram schematic symbols.

Fuse Wiring Diagram For Heated Mirrors and Back-up Lamps Figure 4-60 Fuse wiring diagram indicating fuse F5 supplies the mirror heat and back-up lamp circuits.

Using Peak Hold to Find Intermittent Short Figure 4-63 Using peak hold with DMM ohmmeter to find intermittent short.

Test Light Indicating Presence of Voltage Figure 4-65 Test light indicating presence of voltage.

Normal Voltage Readings Figure 4-66 Circuit with no defects, open switch and closed switch.

Summary Truck wiring is divided into a series of sections called harnesses. Harnesses are mated using connectors. Connectors contain terminals the provide the electrical contact between sections of wire. Wire diameter for North American - built trucks is typically defined by the AWG number. The smaller AWG number, the larger the wire diameter.

Summary (continued) Wire has resistance. The resistance of wire is directly proportional to the wire length and inversely proportional to the wire diameter. The frame rails, sheet metal, and other metal components of a typical truck are called chassis ground. The negative battery terminal is connected to the chassis ground. The chassis ground acts as a conductor for many truck electrical circuits.

Summary (continued) Wiring harness routing refers to the placement of a wiring harness on a truck. Clipping is the attachment method used to attach the harness to the truck. Electric switches are devices used to interrupt the flow of current in a circuit. There are many types of switches. The functionality of a particular switch can be defined by the terms pole and throw.

Summary (continued) Normal state of a switch describes momentary contacts that are open or closed when the switch is not depressed or otherwise disturbed. A normally closed switch has continuity until the switch is depressed. A normally open switch has continuity only when the switch is depressed. A closed switch should have close to 0V drop across it; an open switch should have near battery voltage drop across it.

Summary (continued) Relays are electromagnetic switching devices. A small amount of current flow through a coil forms an electromagnet. The electromagnet causes the relay contacts to open or close, in much the same way as a switch. A relay is like a remotely controlled switch. Relay control circuit describes the electrical circuit that powers the relay. When a positive voltage source and ground are provided by the relay control circuit, the relay coil is energized.

Summary (continued) Circuit protection devices are designed to protect the truck’s wiring harness. Circuit protection devices include fuses, circuit breakers, and fusible links. Inrush or surge describes the high level of current that is drawn by some devices for a brief period of time when first switch on, such as motors and light bulbs. Surge current may be many times greater than the normal current drawn by a device after a brief period of time.

Summary (continued) Adding additional loads such as lights to a circuit causes the current through the circuit protection device to increase. Never replace a circuit protection device with one that has a higher rating than the OEM’s recommendation. Fuses are single use devices that have an element designed to open when the current flow through the fuse exceeds the fuse rating. A combination of time and current cause the element to open.

Summary (continued) Circuit breakers use a bimetal strip to open a set of normally closed contacts. The three main classes of circuit breakers are SAE Type I, Type II, and Type III. Fusible links are made of wire with a special insulated material designed not to burn. The fusible link is designed to be the smallest wire gauge in the circuit that it is protecting.