Electrical Wiring Diagrams Learning Outcomes
Describe various components of a wiring schematic. (i.e wire markings, wire size, symbols of components, grounds, relationship between components and circuits, power distribution)
Identify various electrical symbols. (SAE, DIN, Valley Forge)
Describe how to read wiring schematics.
Describe various uses of electrical schematics.
Describe the differences between various types of e lectrical schematics. (Pictorial, isometric, block, schematic and wiring diagrams, power and ground distribution)
Trace electrical circuits within a schematic.
Recommend diagnostic strategies using electrical schematics and test equipment.
Wiring Diagrams In 1950 there were approximately 200 electrical circuits in a truck. Today there are over 3,000 circuits found in HD commercial vehicles. In 1950, the main interest was the starting, ignition and lighting circuits. Now electronic controls applied to every vehicle system and networked electrical systems have added far more complexity to today’s vehicles. Added to traditional vehicle systems are convenience devices such as navigational and multimedia devices, vehicle safety and security systems, custom body builder circuits and so on. Correctly understanding and interpreting a wiring diagram is important to a technician in order to reduce diagnostic time for electrical problems and eliminate guesswork. A wiring diagram will typically allow a technician to trace circuits from power supplies through switches, components, circuit protection device, harnesses, junction blocks, connectors conn ectors and grounds. Wiring diagrams are arranged by manufacturers in a number of different styles to show with a high degree of clarity individual circuit components and their locations. Types of wiring diagrams include: Map Pictorial Schematic DIN (Deutsche Institute Norm) Valley Forge
Map Diagrams Map diagrams show the entire vehicle wiring circuit. Symbols for components are usually pictorial meaning the symbol looks like a component it represents. Individual components and their spatial relationship to one another are not necessarily conveyed as clearly as logical legible presentation of circuit operation. A variation of the map diagram is the linear diagram. These
use pictorial representations with a mixture mixture of schematic symbols and internal wiring. wiring. A linear diagram may start on one page and continue onto several more a map out individual circuits with a separate diagram.
Above - A pictorial or map diagram of the electrical system of a 1968 Ford.
Schematic Diagrams Schematics are line drawings that explain how a system works by using symbols and connecting lines. Several different standards for schematic diagrams exit DIN and Valley Forge are the most common. Symbols are used to represent devices or components of both simple and complex electrical and electronic systems. Schematic diagrams present a great deal of information in a small amount of space and the reading of schematic symbols requires practice. A logical, step by- step approach to using schematic diagrams for troubleshooting begins with the technician's understanding of the complete system. Schematic circuit diagrams may be supplemented with diagrams, tables, graphs or descriptions. Current path are arranged to show signal or mechanical action from left to right and or top to bottom. Block diagrams are used to represent complex electronic circuitry such s uch as a electronic control modules. On these devices, no internal circuitry circuitry is shown and only inputs or outputs are are depicted. Dotted lines may represent an area or some mechanical action taking place with a component The two most common types of schematic diagrams used today are: Valley Forge DIN (Deutsche Institute Norm)
SAE symbols are used by Valley Forge where DIN symbols are used together with DIN diagrams. terminal connections DIN diagrams are used by many heavy-duty manufacturers. Symbols, terminal numbers, line symbols, operational status in these diagrams are defined by a DIN standard. These diagrams may be accompanied by illustrations showing internal circuitry of some devices and reference coordinates used to assist locating components. Valley Forge wiring diagrams are similar in content to DIN diagrams however SAE coding and symbol are used. Conductor sizes, symbol representations, component and terminal designations are different from DIN standards.
Above – An example of a linear/pictorial wiring diagram.
Vehicles today are wired using sections known as looms or harnesses. Harnesses are prewired for sections of a vehicle. The harnesses are enclosed into protective loom and taped so it is not possible to completely trace a single wire to find a problem. Schematic diagrams are needed to check the circuit at strategic points.
Right –Valley Forge schematic diagram. Left - Designating a wire by circuit number, harness, colour and diameter.
DIN Also called “Current Track” wiring diagrams, they show the power source at the top of the page and the ground points at the bottom. Situated between power and ground are current tracks which contain electrical components and conductors. This current track layout simplifies the wiring diagram. Conductor symbols crossing where they do not connect is kept to a minimum. Power Distribution - Relay Panel The central/relay panel is indicated in gray at the top of the wiring diagram page. The central/ relay panel includes common power circuits, such as battery power (30), ignition switched power (15), load reduction (75/X), and ground (31). All ground connections, whether they occur as a splice in a harness, or the final ground source, are numbered and identified in the wiring diagram. Conductors & Components Between the central/relay panel and the vehicle ground at the bottom of the diagram are located the component symbols and conductors. Components are marked with a component code listed in the legend. Conductors are generally marked with wire color and size. Current Tracks Individual current tracks are identified numerically along the base of the wiring diagram. These numbers are used to find the continuation of a conductor. Where the system or circuit layout is complex, this continuation may be on the same page, or on a different page. For example, the number 191 inside a small box on one page indicates that the wire is continued on current track 191 on the next page with the same color and size of wire with a small box.
Elements of a Wiring Diagram DIN diagrams are representative of all wiring diagrams in use today. Every circuit needs a minimum of the following to operate: Power supply Load Ground Conductors (usually wire) Circuit Protection (Fuse, virtual fuse)
If any of these are missing, a complete circuit is broken and the load will not function. The ability to break down a circuit into its individual parts is the key to being able to diagnose failures in the circuit. Wiring diagrams incorporate many symbols used to illustrate a complete circuit. These symbols can include: Current track numbers Components Terminal designations Conductors Connectors
Together these components make up a complete and accurate wiring diagram. Graphical representations called "symbols" are used to represent components and conductors in wiring diagrams. The key to reading wiring diagrams is understanding the symbols. These symbols are standardized, allowing quick recognition of various components.
DIN Standard 72 552 This standard applies to the terminal designations for circuits. The purpose of the terminal designation system is to enable accurate connection identification from conductors (wires) to various components when diagnosis and repair is necessary. Examples of DIN standards for terminal designations are: 15 Ignition switched on and start 30 Battery + [Type a quote from the document or the summary of an of an interesting point. You can position 31 Ground [Type
the text box anywhere in the document. Use the Text Box Tools tab to change the formatting of the of the pull quote text box.]
31b Switched Ground 50 Starter control switched on only
Wiring Wires are conductors that carry current to components, and are usually indicated by a solid line. A wire shown as a dashed line in a wiring diagram indicates that the wire does not apply to all vehicles and is noted in the wiring diagram legend. Wire colors Knowing the standards for wiring colors makes the job of reading and interpreting them easier. Some of the common standards include wiring color for specific circuits, as well as the terminal designation.
For example: Red . . . . . . . . . . . . . . . . . . . Battery + Green. . . . . . . . . . . . . . . . . . Ignition (1) Brown . . . . . . . . . . . . . . . . . Ground (31) Yellow . . . . . . . . . . . . . . . . . Headlights (58) Wire colors are shown as abbreviations of the Ge rman word for the color. bl . . . . . . . . . . . . . . . . . . . . . Blue br. . . . . . . . . . . . . . . . . . . . . Brown ge . . . . . . . . . . . . . . . . . . . . Yellow gn . . . . . . . . . . . . . . . . . . . . Green ro. . . . . . . . . . . . . . . . . . . . . Red sw . . . . . . . . . . . . . . . . . . . . Black li . . . . . . . . . . . . . . . . . . . . . Violet ws . . . . . . . . . . . . . . . . . . . . White
Wire Gauge Tool
Wire Sizes Wiring diagrams also indicate the wire gauge used (shown in mm2), designating the cross sectional area of the wire. Because Becau se standards exist for the maximum permissible voltage drop across a circuit, wire gauge is critical. If the voltage drop across the wire is too high, one or more of the following may occur: The circuit may overheat The load may not operate properly (due to low voltage condition) Components may be damaged
If a wiring repair needs to be made and metric sized wire is not available ava ilable use American Wire Gauge (AWG) sized wire. Note: If the exact size wire is not available for a repair, use the next larger size.
Connector Pin Assignments Wiring diagrams tell the user at which pin numbers the wires terminate, simplifying diagnosis. There are 4 main types of terminal designations: Push-on/multi-point connections Component/multi-point Central/relay panel Relay
Generally, pin assignments are labelled on the plastic hard-shell connector housing and/or the corresponding component. On larger connectors, pin assignments are labeled at either end of a row. For example, the Engine Control Module (ECM) plug often has 4 to 10 rows of 12 or more terminals. Each row will be marked on each end to facilitate easier diagnosis. Components Components in wiring diagrams are given an alphanumeric designation for identification. The first portion of the code separates the component into basic groups. An F for example, designates a switch, while a Z would be used for a heating element.
Complex Symbols Often the internal schematic of the component is shown to allow the technician to follow current flow through the component. These internal symbols are a combination of several basic symbols. This allows the technician to take a more complex symbol and break it down into its smaller components. Even the most complex components are nothing more than a combination of smaller basic symbols. More complex components may contain complex control circuitry. This will be indicated with the symbol of a transistor in the component symbol (see control module).
A schematic symbol for a control module
A combined component
A relay is an example of a combination of symbols in a single component. Relays require a signal from an outside source to activate. Relays share the component designator “J” with control units. The basic 5-pin relay (below) contains two separate components: a switch and a solenoid. The coil in the solenoid is energized with low current, creating a magnetic pull that closes or opens the switch. Note: All switches and relays are shown in a non-operated state.
Relay schematic symbols. Mechanical action is always left to right – note the the right relay switch closes when energized.
DIN Symbols
SAE Symbols
Valley Forge - GM, Ford
