• List the meaning of symbols used with OPE electrical systems.
• Explain how equipment manufacturers use wire color codes to identify different OPE systems.
• Explain what a wiring harness is used for.
• Describe electrical diagrams and wiring diagrams.
• Explain how to read and use diagrams used with OPE electrical systems.
Electrical systems used with outdoor power equipment (OPE) have diagrams and schematics available for identifying components, tracing circuit paths, and troubleshooting individual OPE operating systems. A successful technician must have a fluent understanding of the symbols used with schematics and diagrams. Each OPE manufacturer uses their own set of standardized wire colors. Technicians will develop an understanding of manufacturer-specific standards as they gain experience.
A
THROUGH GROMMET
EARTH GOES THROUGH DISCONNECT
THROUGH STEERING COLUMN
JUNCTION
CONNECTED
service manuals.
equipment.
are also used on components
Figure 7-1. Symbols used in
electrical and electronic diagrams
a simpli fied
of
various components in a
CIRCUIT
MALE
FEMALE
SINGLE-ELEMENT
DUAL-ELEMENT
SOCKET
ROTARY
SINGLE POLE, SINGLE THROW (SPST)
SINGLE POLE, DOUBLE THROW (SPDT)
POLE, SINGLE THROW (DPST)
POLE, DOUBLE THROW (DPDT)
Using symbols enables easier understanding of circuit operation and logic. To troubleshoot, repair, or replace OPE components, the actual component that the symbol represents must be known. For example, on a schematic diagram, the symbol for a battery is a series of long and short lines. See Figure 7-2. The symbol appearance is different than the actual ap pearance of the battery that is installed in a circuit. Most original equipment manufacturers (OEMs) use IEEE 315, Graphic Symbols for Electrical and Electronics Diagrams, which is also known as the ANSI Y32.2 standard.
Figure 7-2. On a schematic diagram, the symbol for a bat tery is a series of long and short lines.
Most OPE systems are powered by direct current (DC) power supplies. Color coding for DC power circuit wiring depends on the function and the loca tion (country) of the wiring. Most OPE manufacturers have their own specific color-coding requirements for electrical wiring.
When tracing wiring, it is important to know that most OPE has black wire for ground wire and red wire for power supply wire. To acquire a complete set of wir ing codes, the owner/operator manual from the specific manufacturer should be referred to. Every OEM-specific wiring diagram has its own color-coding abbreviations. For example, color codes used with Briggs & Stratton equipment may be different than those used with MTD equipment. See Figure 7-3.
NOTE:
Color Black
Brown Red Orange Yellow Green
Dark green
Light green Blue
Dark Blue
Light Blue
Pur ple Gray White
Abbreviation
BLK or BK
BRN or BN
RED or R
ORG or O
YEL or Y
GRN or G
DK. GRN or DG
LT GRN or LG
BLU or B
DK. BLU or DB
LT BLU or LB
PUR or P
GRY or GY
WHT of W
Figure 7-3. Every OEM-specific wiring diagram has its own color-coding abbreviations.
A wiring harness is a bundle of wires that distrib utes electric power throughout a piece of OPE. See Figure 7-4. Modern equipment such as lawn tractors, utility vehicles, and similar equipment have an abun dance of accessories and components that are electrically powered. The primary source of the electrical power required is the alternator. A secondary power source is a battery, which provides power for starting the engine, stores power for when the power draw exceeds the capacity of the alternator, and absorbs/buffers system noise in the electrical system, which is typically 12 V.
When the engine is in operation, the battery is charged by the engine’s alternator. Before power is distributed, the electricity flows through circuit protec tion devices. The circuit protection devices, which can be fuses, circuit breakers, or fusible links, are generally as close to the battery as possible to prevent damage to the components or wiring from an overcurrent draw.
Since various OPE manufacturers have different engine designs, which also change over time, wiring harnesses are often unique to the year, make, and model of a specific piece of equipment. Wiring harnesses can degrade over time and require repair or replacement because of their proximity to the engine as well as exposure to dirt, mois ture, ultraviolet rays from the sun, heat, and chemicals. Conduits and looms protect harnesses from exposure to these contaminants. Harnesses also can be damaged by physical contact with moving parts, engine vibration, and corrosion from moisture.
Figure 7-4. A wiring harness is a bundle of wires that distributes electric power throughout a piece of OPE.
A wiring harness provides a series of connections that allow experienced OPE mechanics and owners to narrow down problems to specific systems and electrical con nections, making it easier to work on the electronics of the unit. Components commonly connected to a wiring harness include the on-board diagnostic computer, fuelinjection systems, and lights. On many wiring harnesses, the connectors and wires that connect these systems may be changed for repair and replacement.
Most wiring harnesses have connectors that plug into a machine’s electrical components, which allows for quicker repairs. For example, if an electric clutch fails, the connectors can be unplugged, the clutch replaced, and the connectors for the new clutch plugged back in to the machine. Note: While electrical connectors can make repairs easier, the connectors can also be a source of problems if they degrade from dirt, moisture, UV rays, heat, chemicals, or excessive force.
An electrical diagram is a document that shows the function of a single circuit or of several circuits. Electrical diagrams are basically maps of how power is supposed to move through a circuit or a device or component, whereas wiring diagrams strictly show the physical wiring of entire circuits. The three types of electrical diagrams commonly used in the OPE in dustry are schematic diagrams, functional diagrams, and block diagrams.
A schematic diagram is a diagram that shows electrical system circuitry with symbols that depict electrical devices and lines representing the conductors. Schematic electrical wiring diagrams are drawn at the engineering level. They are drawn based on the path of electron flow without regard to the physical location of components in relation to one another. See Figure 7-5.
Schematic diagrams can be difficult to follow when a single component is used in multiple circuits. An example of this is an electric power take-off (PTO) switch. Most electric PTO switches are connected to three separate circuits: the start, PTO, and safety circuits. In a schematic drawing, it will look like three separate switches, scattered across the drawing, with all three labeled as “PTO switch.” However, all three of these switches are not separate switches, but rather they are three parts of one physical switch.
A functional diagram is a diagram that represents the functional relationships of the parts of a system. A functional diagram is the most common type of electri cal diagram. Unlike a schematic diagram, it depicts the physical components. For example, with a PTO switch, unlike the schematic diagram where all three parts of a PTO switch are separated in the drawing, all three parts would be drawn together in a box to symbolize one switch. Functional diagrams are useful for finding faults in a system where one circuit can be shorted to another circuit. Functional diagrams are used to locate a component or device by identification of the physical component, show how components are connected, and show the functional relationships of components within a circuit or a system. See Figure 7-6.
Figure 7-6. Functional diagrams are useful for finding points in a system where one circuit can be shorted to another circuit.
Functional diagrams can be used to understand the functional relationships of each component used in a particular OPE system.
A block diagram is a type of electrical diagram that shows the relationship between individual sections, or blocks, of a circuit or system. The circuit inside each block is not shown. Instead, text describes the function of the block. This solves the problem of showing com plicated circuits.
Block diagrams protect proprietary information (exact device or component information) that a manu facturer may not want to release. Block diagrams show the contents of a circuit, device, or component. In block diagrams, the components within the circuit are repre sented by a series of shapes that represent the compo nents within the system. See Figure 7-7.
Electrical diagrams provide guidance on the function, assembly, and service of an electrical circuit. Without an electrical diagram, only an unidentified grouping of components and wires would be presented to the user or service technician. An electrical diagram allows the user or service technician to understand the circuit function and become familiar with how the desired effect of the electrical circuit is achieved.
725-0150 725-0122 725-0514 725-0267 725-0819 725-0759 725-0925
Ground wire— 11.5
Electric wire (Red)— 11.5
Electric wire— 7.25
y
Ignition switch Safety switch (blade) Spring switch (reverse)
725-0268 725-0222 725-1024 722-0135 725-0771 725-1023
PartDescription
Light switch Safety switch (clutch)
Ground wire
strip Solenoid Wire har ness Comp
shows the relationship between individual sections, or blocks, of a circuit or system.
A block diagram is a type of electrical drawing
There are a variety of symbols on an electrical diagram that represent actual components and wires. An under standing of these symbols is required to properly read an electrical diagram. In addition to understanding symbols, an OPE technician must also be proficient in the following:
Understand grounding in electrical circuits. Ground is a common reference point that electrical dia grams use to show the overall unity of the various functions of a circuit. It does not refer to the actual ground of the earth. Ground symbols are either a triangle pointing down, a set of three parallel lines decreasing in length (earth ground), or a threepronged fork (chassis ground).
Understand that lines in an electrical diagram are representations of wires. Wires are used in actual circuits to connect devices together. All points along the wire are identical and connected. Wires may cross each other on an electrical diagram, but that does not necessarily mean that they are connected. If wires are connected, the diagram will show lines intersecting at an angle and a dot will be shown at the point where the lines intersect. If wires are not connected, the diagram will show lines inter secting without a dot or one wire will be shown looping around the other wire in a semicircle. See Figure 7-8.
Figure 7-8. If wires are connected, an electrical diagram will show lines intersecting at an angle and a dot will be shown at the point where the lines intersect.
• Identify resistors using symbols. Resistors impede the flow of current to an extent determined by the resistance value. Resistors are used to scale and shape the electrical signal and are typically rated in ohms ( Ω ).
• Identify switches and relays. Understand how a switch stops or redirects the current upon opening or closing the switch and how a relay controls another circuit to allow current flow to a work device.
• Identify capacitors using symbols. Capacitors are an energy storage device. They function in an electrical
system the same way an accumulator does in a hy draulic system. A capacitor will store electrons when the voltage going to it is higher than the voltage of the capacitor, and it will drain off voltage if the voltage is higher than that of the circuit it is connected to. Capacitors absorb and discharge charges very rapidly, making them extremely useful for filtering system noise or smoothing voltage ripples.
• Understand that a capacitor’s energy storage properties only function in DC circuits. In AC circuits, the capacitor is considered shorted.
• Understand the meaning of nonstandard symbols. Nonstandard symbols are typically a geometric shape, usually a rectangle, with a device indicator number or description in or beside the shape. Sometimes when a wire contacts a device, there is a number or letter indicated at the connection point.
• Find the location of capacitors and resistors in a circuit. Refer to the service manual for the circuit to find the values of capacitors and resistors and the part numbers of the installed devices.
• Determine the circuit tasks performed by circuit devices. To determine the circuit tasks, acquire and read the manufacturer service manual for each individual device.
• Identify the circuit function. Based on the electrical diagram, isolate the function of each circuit compo nent. This will determine the operation of the circuit.
A wiring diagram is a simplified pictorial representa tion of an electrical circuit that is used to show how one individual device or component is wired or to show how all the devices and components of a circuit or system are wired together. Wiring diagrams are typically included with most service manuals. See Figure 7-9.
Figure 7-9. A wiring digram is a simplified representation of an electrical circuit.
Wiring diagrams show how control and power circuits are connected together. Internal and external connections are shown in sufficient detail for the technician to make or trace back connections. Wiring diagrams are used in troubleshooting because wiring diagrams indicate the actual device and component layout with all connections.
Wiring diagrams often show the actual circuit loca tion of each device and component. For example, a wiring diagram will typically show that the PTO switch and key switch are located in opposite locations. Sepa rate systems are indicated by dashed lines around the pushbuttons. See Figure 7-10. The wiring diagram also shows the normal position of each pushbutton.
Symbols used on wiring diagrams may be the same symbols used with electrical diagrams, or they may be simple rectangles and circles. No attempt is made to show exact sizes or shapes of devices and components on wiring diagrams. For example, terminal connections can be shown as circles even when the physical appear ance of a terminal differs. The circuits that are found on a wiring diagram include the following:
• ignition system
• charging system
• electric starting system
• operator-presence control system
• accessory systems (such as horns and lighting)
An ignition system provides a high-voltage spark in the combustion chamber at the proper time. Although several variations of ignition systems exist, the function of each system is essentially the same. Single-cylinder engine ignition systems are less complex than multiplecylinder engine ignition systems.
A charging system is a system that replenishes the electrical power drawn from a battery during starting and accessory operation. An alternator, which is a device that is sometimes used in conjunction with a regulator/ rectifier, maintains the battery at full charge and supplies electricity for accessories such as lights and electric lifts. Drawings and diagrams describing the charging system and components follow the traditional positiveto-negative current flow convention commonly used in the OPE industry.
An electric starting system is a group of electri cal components that, when activated by the operator, rotates a crankshaft to start an engine. Electric starting systems vary depending on design and application. Larger single-cylinder and multiple-cylinder engines commonly require an electric starting system. Electric starting systems commonly include a starter motor, starter solenoid, ignition switch, and battery.
An operator-presence control system is a system used to ensure the safe positioning of the equipment operator in relation to the equipment. Operator-presence control systems contain switches that are typically single-throw, single- or double-pole. Applications of operator-presence control switches include ensuring that the operator is seated on equipment, has proper hand control, is in a safe operat ing position for equipment use, and can stop the machine from operating when safety requirements are not met.
An accessory system is a system used to control a supplemental piece of equipment. Accessory systems in clude headlights, PTOs, low-oil warnings, audible alarms for indicating overheating, and hour meters. Although some of the accessory electrical circuits can be integrated into more complex switches, the majority of accessory switches are single-pole, single-throw (SPST) switches.
A wiring diagram is essentially the same as an electrical diagram. The main difference between the two is that the ends of the wires depicted on a wiring diagram are shown in the actual position that they would be on the unit. On an electrical diagram, only the path of electricity is shown. See Figure 7-11. Splices and connections in a wiring diagram mirror the actual wiring. Wiring dia grams can be read by matching the actual components and devices on the unit to those pictured.
Many OEMs of OPE utilize different types of wiring diagrams. Always carefully review wiring diagrams when working on different equipment to identify any differences in diagrams.
Figure 7-10. The OPE circuits that are found on wiring diagrams include ignition systems, charging systems, electric starting systems, operator-presence control systems, and accessory systems.
Figure 7-11. The ends of the wires depicted on a wiring diagram are shown in the actual position that they would be on the unit. On an electrical diagram, only the path of electricity is shown.
For an OPE technician to properly service equip ment, the technician must understand electrical symbols, electrical diagrams, and wiring dia grams. Wire color codes are used to trace circuit paths and wiring harness installations. An elec trical diagram shows the function of a separate circuit or of several circuits. A wiring diagram is a type of drawing that shows the connection of input devices and output components in a circuit.
What
What
8. What is the best source for OPE wiring color codes?
9. How are wires identified in a schematic diagram?
10. In addition to understanding symbols, list nine skills related to electrical circuits that a technician must be proficient in.
11. List five OPE circuits typically found on a wiring diagram.
12. What is an electr ic starting system?
13. What is a charging system?
14. What is an operator-presence control system?
15. What is an accessor y system?
1. The following symbol represents a ___.
A. fuse
B. circuit breaker
C. resistor
D. diode
2. The following symbols represent a ___.
A. relay
B. transformer C. capacitor D. switch
3. The following symbol represents a ___.
A. diode
B. fuse C. circuit breaker D. switch
4. The following symbols represent a ___. A. diode
B. resistor C. solenoid D. fuse
5. The following symbol represents a(n) ___ switch. A. SPST
B. SPDT C. DPST D. DPDT
6. The following symbol represents a(n) ___ switch. A. SPST B. SPDT C. DPST D. DPDT
7. The following symbol represents a ___.
A. spar k plug B. solenoid C. coil D. diode
8. The following symbol represents a(n) ___. A. alternator
B. PTO clutch C. regulator D. ignition coil
9. The following symbol represents wires that ___. A. cross but are not connected B. are connected
C. are solid only D are stranded only
10. The following symbols represents a(n) ___. A. battery
B. alternator
C. electr ic motor D. capacitor
11. The following symbols represents a(n) ___.
A. coil
B. chassis ground C. spar k plug
D. ear th ground
12. The following symbols represents a(n) ___.
A. diode
B. light
C. stator
D. electr ic motor
13. The following symbol represents a ___.
A. dual element light
B. railroad crossing
C. single element light
D voltmeter
14. A ___ is a pictor ial drawing of a harness showing the location of all electrical components, connectors, harness grounds, and harness clamp locations.
A. component location drawing
B. functional diagram
C. wir ing diagram
D. wir ing harness drawing
15. The following symbol represents a ___.
A. bulb I.D.
B. junction point
C. pin and socket connector
D. splice I.D.