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

2. 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

3. 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

4. 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

5. 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

6. Typical Wiring Harness
Figure 4-1 Typical wiring harness.

7. 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.

8. 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

9. Stranded Wire
Figure 4-2 Stranded wire.

10. 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

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

12. 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

13. 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

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

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

16. 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

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

18. 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.

19. 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.

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

21. 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.

22. 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.

23. 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

24. Knife Switch
Figure 4-22 Knife switch.

25. 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)

26. 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

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

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

29. Relay Components
Figure 4-33 Relay components.

30. 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

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

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

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

34. 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

35. 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

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

37. 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

38. 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

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

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

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

42. 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

43. 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.

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

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

46. 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.

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

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

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

50. 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.

51. 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.

52. 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.

53. 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.

54. 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.

55. 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.

56. 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.

57. 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.