Welcome to Lesson 8! 🎉
レッスン8へようこそ！
In this comprehensive lesson, you will master the essential skills of reading wiring diagrams, using multimeters, and performing systematic electrical troubleshooting.
この包括的なレッスンでは、配線図の読み方、マルチメーターの使用法、体系的な電気故障診断の重要なスキルを習得します。
✓ Wiring diagram types and symbols
✓ Circuit tracing techniques
✓ Multimeter operation and measurements
✓ Voltage drop testing
✓ Systematic troubleshooting methods
✓ Common electrical faults and repairs
This lesson takes approximately 6-8 hours to complete, including hands-on practice and the quiz.
Complete Lessons 1-7 before starting. Strong understanding of electrical fundamentals is essential.
Types of Wiring Diagrams 📊
配線図の種類
Automotive manufacturers use several types of diagrams to represent electrical circuits.
自動車メーカーは、電気回路を表すためにいくつかの種類の図を使用します。
• Shows electrical connections and component relationships
• Uses standardized symbols
• Does not show physical location
• Best for understanding circuit operation
• Most common type for troubleshooting
• Shows physical location of components
• Indicates connector positions
• Helps locate components in vehicle
• Often combined with schematic info
• Useful for finding parts
• Shows pin assignments in connectors
• Indicates wire colors at each pin
• Essential for testing at connectors
• Often shows connector view orientation
• Terminal identification
Wiring Diagram Formats 📄
配線図のフォーマット
• Power flows from top to bottom
• Ground at bottom of diagram
• Easy to trace current path
• Shows complete circuits
• Common in European vehicles
• Shows one system at a time
• Includes all related components
• Easier to understand single system
• May span multiple pages
• Common in Japanese vehicles
• Letters across top (A, B, C…)
• Numbers down side (1, 2, 3…)
• Locate components by grid reference
• Cross-references between pages
• Example: “See C-5 for ground location”
Basic Electrical Symbols ⚡
基本的な電気記号
Understanding standard symbols is essential for reading wiring diagrams.
標準記号の理解は配線図を読むために不可欠です。
• JIS: Japanese Industrial Standard (日本工業規格)
• DIN: German Industrial Standard
• SAE: Society of Automotive Engineers
• ISO: International Organization for Standardization
Component Symbols 🔧
部品記号
• Solid dot (●): Wires are connected
• No dot (crossing lines): Wires cross but don’t connect
• Splice (◆): Factory wire splice location
• Shield: Shielded wire for EMI protection
• Numbers: Pin numbers in connectors
• Letters: Terminal designations (B+, IGN, ACC)
• Colors: Wire color codes
• Gauge: Wire size (0.5, 0.85, 1.25 sq mm)
Wire Color Codes 🎨
配線色コード
Japanese vehicles use standardized wire color codes to identify circuit functions.
日本車は回路機能を識別するために標準化された配線色コードを使用します。
| Color | 色 | Abbreviation | Common Use | 用途 |
|---|---|---|
| Black | 黒 | B | Ground circuits |
| White | 白 | W | Ground, ignition |
| Red | 赤 | R | Battery positive, power |
| Yellow | 黄 | Y | Ignition switched power |
| Green | 緑 | G | Lighting circuits |
| Blue | 青 | L | Headlights, indicators |
| Orange | 橙 | O | Accessory circuits |
| Brown | 茶 | BR | Tail lights |
• Format: Base color / Stripe color (例: R/W = Red with White stripe)
• Example: G/Y = Green with Yellow stripe
• Reading: First letter is main color, second is stripe
Circuit Tracing Basics 🔍
回路追跡の基本
Circuit tracing is the systematic process of following electrical paths through a wiring diagram.
回路追跡は配線図を通じて電気経路を追跡する体系的なプロセスです。
1. Identify power source: Find battery or fuse
2. Follow positive path: Trace from power to load
3. Identify load: Find the component being powered
4. Follow ground path: Trace from load to ground
5. Note all components: Switches, relays, connectors
• Power source: Battery or switched power
• Protection: Fuse or circuit breaker
• Control: Switch, relay, or module
• Load: Light, motor, or other device
• Ground: Return path to battery negative
Power Distribution 🔌
電源分配
Understanding power distribution is essential for tracing circuits.
電源分配の理解は回路追跡に不可欠です。
• B+ (Battery): Constant power, always hot
• IGN (Ignition): Power when key in ON/RUN
• ACC (Accessory): Power in ACC and ON positions
• ST (Start): Power only during cranking
• IG2: Secondary ignition circuit
• Under-hood fuse box: High-current circuits, relays
• Interior fuse box: Accessory and body circuits
• Relay box: Contains relays and fuses
• Junction block: Power distribution center
• Mini fuse: Small blade type (common)
• Standard fuse: Regular blade type
• Maxi fuse: Large blade for high current
• Fusible link: Wire-type protection
• Cartridge fuse: Bolt-in type
Digital Multimeter (DMM) 🔬
デジタルマルチメーター
The digital multimeter is the most important tool for electrical troubleshooting.
デジタルマルチメーターは電気故障診断で最も重要なツールです。
• DC Voltage (DCV): Measure battery, sensors
• AC Voltage (ACV): Measure alternator output
• Resistance (Ω): Measure components, continuity
• Current (A): Measure circuit amperage
• Continuity: Check wire integrity
• Diode test: Check diodes and LEDs
• Black lead: Always in COM (common) jack
• Red lead: V/Ω jack for voltage and resistance
• Red lead: A jack for current measurement
• Important: Never measure current in voltage mode!
• Check meter rating (CAT III for automotive)
• Inspect leads for damage before use
• Start with highest range if unsure
• Never measure resistance on powered circuits
• Use proper PPE when working with batteries
Voltage Measurement ⚡
電圧測定
Voltage measurement is the most common electrical test performed.
電圧測定は最も一般的な電気テストです。
1. Set meter to DC Volts (DCV)
2. Select appropriate range (20V for automotive)
3. Connect black lead to known good ground
4. Touch red lead to test point
5. Read voltage on display
• Battery (engine off): 12.4-12.7V
• Battery (engine running): 13.5-14.5V
• Ignition ON circuits: 11.5-12.5V
• Ground circuits: 0V (or very close)
• 5V reference: 4.9-5.1V
• Full voltage: Power is reaching test point
• No voltage: Open circuit before test point
• Low voltage: High resistance in circuit
• Fluctuating: Intermittent connection
Resistance Measurement Ω
抵抗測定
Resistance measurement checks component condition and wire integrity.
抵抗測定は部品の状態と配線の完全性をチェックします。
ALWAYS disconnect power before measuring resistance!
Measuring resistance on a powered circuit can damage the meter and give false readings.
抵抗測定前に必ず電源を切断してください！
1. Disconnect power to circuit
2. Set meter to Ohms (Ω)
3. Isolate component if needed
4. Connect leads across component
5. Read resistance value
• 0 Ω (or very low): Good continuity, short circuit
• Specified value: Component is good
• OL (Over Limit): Open circuit, infinite resistance
• Higher than spec: Increased resistance, degraded
• Good wire: Less than 1Ω
• Ignition coil primary: 0.5-2Ω
• Injector: 12-16Ω
• Relay coil: 50-100Ω
• Temperature sensor: Varies with temp
Current Measurement 🔄
電流測定
Current measurement determines how much electricity is flowing through a circuit.
電流測定は回路を流れる電気量を測定します。
Current is measured IN SERIES with the circuit!
The meter must be connected so all current flows through it. Wrong connection can blow the meter fuse or damage the meter.
• In-line measurement: Break circuit, insert meter
• Clamp meter: Clamp around wire (non-invasive)
• Fuse method: Remove fuse, connect meter across
• Shunt resistor: Measure voltage across known resistance
• Parasitic draw: Find battery drain
• Motor current: Check motor condition
• Circuit load: Verify proper operation
• Starter current: Diagnose starting problems
• Charging current: Check alternator output
Voltage Drop Testing 📉
電圧降下テスト
Voltage drop testing is the most effective method for finding high-resistance problems in circuits.
電圧降下テストは回路の高抵抗問題を見つける最も効果的な方法です。
• Voltage “used up” by resistance in a circuit
• Measured while circuit is operating under load
• Reveals problems invisible to other tests
• Shows exactly where resistance exists
• Essential for diagnosing intermittent problems
1. Circuit must be ON and under load
2. Set meter to DC Volts
3. Connect leads across the section to test
4. Read voltage drop on display
5. Compare to specifications
• Wire/connection (power side): Max 0.2V
• Wire/connection (ground side): Max 0.1V
• Switch contacts: Max 0.3V
• Fuse: Max 0.1V
• Total circuit drop: Should equal source voltage
Voltage Drop Test Points 🎯
電圧降下テストポイント
• Battery + to fuse: Check main power feed
• Across fuse: Check fuse condition
• Fuse to switch: Check wire and connectors
• Across switch: Check switch contacts
• Switch to load: Check remaining power wire
• Load to ground point: Check ground wire
• Ground point to battery -: Check chassis ground
• Across connectors: Check each connection
• Total ground path: Should be less than 0.1V
• Corroded connections: Green/white buildup
• Loose terminals: Poor contact
• Damaged wire: Broken strands
• Undersized wire: Too small for current
• Burned contacts: Switch or relay damage
• Clean corroded connections
• Tighten loose terminals
• Repair or replace damaged wires
• Replace faulty switches/relays
• Add ground straps if needed
Continuity Testing 🔗
導通テスト
Continuity testing verifies that a complete path exists for current flow.
導通テストは電流が流れる完全な経路が存在することを確認します。
1. Disconnect power to circuit
2. Set meter to continuity mode (beep symbol)
3. Touch leads together to verify meter works
4. Connect leads to both ends of wire/component
5. Beep = continuity, No beep = open circuit
• Wire integrity: Check for broken wires
• Fuse condition: Good fuse has continuity
• Switch operation: Continuity when closed
• Ground circuits: Path to chassis ground
• Connector pins: Check for bent/damaged pins
• Beep + low ohms: Good continuity
• No beep + OL: Open circuit (break in path)
• Intermittent beep: Loose connection
• Beep where shouldn’t be: Short circuit
Systematic Troubleshooting 🔧
体系的故障診断
A systematic approach ensures efficient and accurate diagnosis of electrical problems.
体系的なアプローチにより、電気的問題の効率的で正確な診断が保証されます。
1. Verify the complaint: Confirm the problem exists
2. Analyze the symptom: Understand what’s happening
3. Isolate the problem: Narrow down the cause
4. Find the root cause: Identify the exact fault
5. Repair the problem: Fix the issue properly
6. Verify the repair: Confirm problem is solved
• Customer interview: When, how often, conditions
• Service history: Previous repairs, patterns
• TSBs: Technical Service Bulletins
• Wiring diagrams: Circuit information
• Scan tool data: DTCs and live data
Common Electrical Faults ⚠️
一般的な電気故障
• Open circuit: Component doesn’t work at all
• Short circuit: Blown fuse, overheating
• Short to ground: Fuse blows immediately
• High resistance: Dim lights, slow motors
• Intermittent: Works sometimes, fails sometimes
Diagnosing Open Circuits 🔓
断線の診断
An open circuit is a break in the electrical path that prevents current flow.
断線は電流の流れを妨げる電気経路の切断です。
• Broken wire: Physical damage, fatigue
• Blown fuse: Overcurrent protection activated
• Bad connection: Corroded or loose terminal
• Failed component: Burned out bulb, open coil
• Disconnected connector: Not fully seated
1. Check fuse first (visual and continuity)
2. Check for voltage at component
3. If no voltage, work backward toward power source
4. Use continuity test on suspect wires
5. Check all connectors in circuit
• Test at middle of circuit first
• If voltage present, problem is after test point
• If no voltage, problem is before test point
• Continue splitting until fault is found
• Efficient for long circuits
Diagnosing Short Circuits ⚡
短絡の診断
A short circuit creates an unintended low-resistance path for current.
短絡は電流の意図しない低抵抗経路を作ります。
• Excessive current flow
• Overheating wires (fire risk)
• Blown fuses
• Damaged components
• Battery drain
1. Remove blown fuse
2. Disconnect loads on circuit
3. Set meter to resistance/continuity
4. Check from fuse terminal to ground
5. Should be OL (open) – if low, short exists
6. Disconnect sections to isolate short location
• Install short finder in place of fuse
• Tool pulses current through circuit
• Use inductive probe to trace wire
• Signal stops at location of short
• Efficient for finding hidden shorts
• Door jamb wiring (flexing damage)
• Under carpet (water damage)
• Near sharp edges (chafing)
• Engine compartment (heat damage)
• After collision repairs
Parasitic Draw Testing 🔋
暗電流テスト
Parasitic draw is the small amount of current that flows when the vehicle is off. Excessive draw causes dead batteries.
暗電流は車両がオフの時に流れる少量の電流です。過剰な暗電流はバッテリー上がりの原因となります。
• Acceptable range: 25-50 milliamps (mA)
• Maximum: Usually under 85 mA
• Sources: Clock, radio memory, ECU keep-alive
• Problem level: Over 100 mA indicates issue
• Severe: Over 300 mA will drain battery overnight
1. Turn off all accessories, close all doors
2. Wait 30-60 minutes for modules to sleep
3. Disconnect negative battery cable
4. Connect ammeter in series (battery to cable)
5. Read current draw on meter
6. If high, pull fuses one at a time to isolate circuit
• BCM: 5-30 minutes to sleep
• Radio: Immediate or 10 minutes
• Security system: May stay active
• Keyless entry: Periodic wake-up
• Tip: Wait for draw to stabilize before testing
• Glove box or trunk light staying on
• Aftermarket accessories (stereo, alarm)
• Faulty alternator diode
• Module not entering sleep mode
• Relay stuck closed
Isolating Parasitic Draw 🔍
暗電流の特定
1. Connect ammeter in series with battery
2. Note the total parasitic draw reading
3. Pull fuses one at a time
4. Watch ammeter for significant drop
5. When draw drops, that circuit has the problem
6. Consult wiring diagram for that fuse’s circuits
• Use DC clamp meter around individual wires
• No need to break circuit
• Faster than fuse pull method
• Can measure at fuse box or component
• Requires sensitive low-amp clamp meter
• Review wiring diagram for that fuse
• Identify all components on circuit
• Disconnect components one at a time
• When draw drops, faulty component found
• Repair or replace as needed
Scan Tool Diagnostics 💻
スキャンツール診断
Modern vehicles require scan tools for comprehensive electrical diagnosis.
現代の車両は包括的な電気診断にスキャンツールが必要です。
• Read DTCs: Diagnostic Trouble Codes
• Clear DTCs: Reset codes after repair
• Live data: Real-time sensor values
• Freeze frame: Conditions when code set
• Bi-directional: Activate components for testing
• Module info: Software versions, VIN
• P codes: Powertrain (engine, transmission)
• B codes: Body (interior, accessories)
• C codes: Chassis (ABS, suspension)
• U codes: Network (communication)
• Format: P0XXX = Generic, P1XXX = Manufacturer
• P0300: Random/Multiple Cylinder Misfire
• P0171: System Too Lean (Bank 1)
• B1421: Driver Door Lock Circuit Open
• C1201: Engine Control System Malfunction
• U0100: Lost Communication with ECM
Using Live Data 📈
ライブデータの活用
Live data allows you to see what the ECU sees in real-time.
ライブデータはECUが見ているものをリアルタイムで確認できます。
• Battery voltage: Should be 13.5-14.5V running
• Coolant temp: Should reach operating temp
• O2 sensor: Should switch between rich/lean
• Fuel trims: Should be near 0% (±10%)
• RPM: Should match tachometer
• Always compare to manufacturer specifications
• Look for values that don’t change (stuck sensor)
• Look for erratic readings (intermittent fault)
• Compare related parameters (should correlate)
• Record data for before/after comparison
• Graph view shows changes over time
• Easier to spot intermittent problems
• Can overlay multiple parameters
• Record and playback for analysis
• Compare to known-good patterns
Intermittent Faults 🔀
間欠的故障
Intermittent faults are the most challenging electrical problems to diagnose.
間欠的故障は診断が最も困難な電気的問題です。
• Problem comes and goes
• May be temperature-related
• May be vibration-related
• May be position-related
• Often difficult to reproduce
• Wiggle test: Move wires/connectors while monitoring
• Heat test: Use heat gun on suspect components
• Cold test: Use freeze spray on components
• Vibration test: Tap on components/connectors
• Road test: Drive over bumps, turns
• Loose connector pins: Spread or backed out
• Corroded terminals: Oxidation buildup
• Broken wire strands: Internal break
• Cold solder joint: Cracked circuit board solder
• Thermal expansion: Component fails when hot
• Record conditions when fault occurs
• Note temperature, humidity, time of day
• Document what was happening (turning, braking)
• Check for patterns in occurrence
• Review customer complaint carefully
Wire Repair Techniques 🔧
配線修理技術
Proper wire repair ensures reliable, long-lasting connections.
適切な配線修理は信頼性の高い長持ちする接続を保証します。
• Solder and heat shrink: Best quality, permanent
• Crimp splice: Quick, reliable if done properly
• Butt connector: Easy but less reliable
• Wire tap: Not recommended for repairs
• Twist and tape: Never acceptable!
1. Strip wire ends 10-15mm
2. Slide heat shrink onto wire first
3. Twist wires together tightly
4. Apply flux and heat with soldering iron
5. Apply solder until it flows into joint
6. Slide heat shrink over joint and heat
• Use same gauge wire or larger
• Use same insulation type (heat resistant if needed)
• Stagger splices to prevent bulk
• Support repaired wires to prevent stress
• Seal all repairs against moisture
Connector Repair 🔌
コネクター修理
Connector problems are a leading cause of electrical faults.
コネクターの問題は電気故障の主な原因です。
• Visual check: Corrosion, damage, moisture
• Pin condition: Bent, spread, pushed back
• Lock tabs: Broken or worn
• Seals: Missing or damaged
• Terminal tension: Should grip tightly
• Cleaning: Electrical contact cleaner
• Tension adjustment: Carefully close female terminals
• Terminal replacement: Use proper release tool
• Dielectric grease: Apply to prevent corrosion
• Seal replacement: Replace damaged seals
1. Use correct terminal release tool
2. Depress locking tab and pull terminal out
3. Cut old terminal off wire
4. Strip wire to correct length
5. Crimp new terminal properly
6. Insert until lock clicks
• Using wrong size terminal
• Poor crimp connection
• Not fully seating terminal
• Damaging connector housing
• Forgetting to apply dielectric grease
Electrical Safety ⚠️
電気作業の安全
Working with automotive electrical systems requires attention to safety.
自動車電気システムの作業には安全への注意が必要です。
• Disconnect battery before working on circuits
• Wait for capacitors to discharge (hybrid/EV)
• Wear safety glasses when working near battery
• Remove jewelry to prevent shorts
• Use insulated tools when possible
• Batteries produce explosive hydrogen gas
• Keep sparks and flames away
• Disconnect negative first, reconnect last
• Use proper jump-start procedures
• Wear gloves and eye protection
• High voltage systems (200-800V) can be lethal
• Only trained technicians should work on HV
• Follow manufacturer disable procedures
• Use HV-rated PPE and tools
• Verify system is de-energized before work
• Safety glasses
• Insulated gloves (for HV work)
• Face shield (battery work)
• Non-conductive footwear
• Fire extinguisher nearby
Lesson Summary 📋
レッスンのまとめ
Congratulations! You’ve learned comprehensive wiring diagram reading and troubleshooting skills.
おめでとうございます！包括的な配線図の読み方と故障診断スキルを学びました。
• Wiring diagrams use standardized symbols and formats
• Wire colors follow Japanese/international standards
• Multimeters measure voltage, resistance, and current
• Voltage drop testing finds high-resistance problems
• Systematic troubleshooting follows a logical process
• Proper repairs ensure reliable, lasting connections
• Battery voltage: 12.4-12.7V (off), 13.5-14.5V (running)
• Max voltage drop (power): 0.2V
• Max voltage drop (ground): 0.1V
• Normal parasitic draw: 25-50 mA
• Relay coil resistance: 50-100Ω
Now it’s time to test your knowledge with a 10-question quiz. You need 70% (7/10) to pass. Good luck!
10問のクイズで知識をテストしましょう。合格には70%（7問正解）が必要です。頑張ってください！
📝 Lesson 8 Quiz
レッスン8クイズ
Test your knowledge with 10 multiple-choice questions.
10問の多肢選択式問題で知識をテストします。
• 10 multiple-choice questions
• Passing score: 70% (7/10 correct)
• You can review your answers after completion
• Take your time and read carefully
Click “Next” to begin the quiz. Good luck!
「次へ」をクリックしてクイズを開始します。頑張ってください！
問題1: 回路のアース側で許容される最大電圧降下は？
正解はA) 0.1Vです。アース側の電圧降下は0.1V未満であるべきです。電源側は0.2Vまで許容されます。
問題2: 配線色コード「R/W」は何を示しますか？
正解はA) 赤に白ストライプです。最初の文字がメインの色、スラッシュの後の文字がストライプの色です。
問題3: 抵抗測定をしてはいけないのはいつですか？
正解はA) 回路に電源が入っている時です。電源が入った回路で抵抗を測定すると、メーターが損傷し、誤った読み取り値が出る可能性があります。
問題4: ほとんどの車両の正常な暗電流範囲は？
正解はB) 25-50 mAです。正常な暗電流は25-50ミリアンペアです。100 mAを超えると問題があります。
問題5: 抵抗測定時にマルチメーターに表示される「OL」は何を示しますか？
正解はA) 断線/無限大抵抗です。OLは「オーバーリミット」を意味し、抵抗が測定できないほど高い（断線）ことを示します。
問題6: 「B」で始まるDTCはどのタイプですか？
正解はA) ボディ（内装、アクセサリー）です。Bコードはドア、ウィンドウ、シート、内装アクセサリーなどのボディシステムに関連します。
問題7: 永久的な配線接続を行う最良の方法は？
正解はA) はんだとヒートシュリンクです。これは最も強く、信頼性が高く、耐候性のある接続を提供します。
問題8: 回路の電流はどのように測定しますか？
正解はA) 回路と直列にです。電流はメーターを通過する必要があるため、直列に接続する必要があります。
問題9: 「半分割法」は何に使用されますか？
正解はA) 断線を効率的に特定するです。回路の中間でテストすることで、どちらの半分に故障があるかを素早く判断できます。
問題10: 配線図の黒丸（●）は何を示しますか？
正解はA) 配線が接続されているです。線の交点にある黒丸は、配線が電気的に接続されていることを示します。
結果を計算中…
You’ve completed Lesson 8 and Module 5! Continue with Module 6 or review your answers below.
