Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Lighting System
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Lighting System
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Subject: Auto Mechanical Works
Class: Senior Secondary 2
Term: 3rd Term
Week: 1
Theme: Safety And Maintenance
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This topic introduces students to the crucial role of the automotive lighting system in vehicle operation, safety, and regulatory compliance. It provides foundational knowledge and practical skills necessary for diagnosing common faults, performing routine maintenance, and ensuring the proper functionality of various lighting components. Understanding the lighting system is vital for automotive technicians in Nigeria, as it directly impacts road safety, vehicle roadworthiness inspections (e.g., by Vehicle Inspection Officers - VIOs), and the ability to diagnose and repair issues in a wide range of vehicles commonly found on Nigerian roads, from private cars to commercial buses and trucks.
voltage indicates an open circuit upstream.
Ground Check (Continuity): Use a multimeter (continuity or resistance mode) to check for a good ground connection at the bulb socket. Place one probe on the ground terminal of the socket and the other on a known good chassis ground. A reading of near zero ohms indicates a good ground. High resistance or open circuit indicates a bad ground.
Switch/Relay Check: Check for voltage input and output at the switch or relay terminals to determine if they are functioning correctly. Worked Example for Fault Tracing (Performance Objective 1): Scenario: A Nigerian driver reports that the left rear tail light of their Toyota Corolla (a common vehicle in Nigeria) is not working. The brake light and turn signal in the same assembly are working fine.
Procedure:
1. Symptom Verification: Confirmed: Left rear tail light is out. Other functions (brake, turn signal) are okay in the same housing. This suggests the issue is specific to the tail light circuit or bulb, not a general power/ground issue to the whole assembly.
2. Visual Inspection: Turn on the parking lights/headlights. Access the left rear tail light assembly. Remove the cover. Inspect the tail light bulb. Often, tail lights use a dual-filament bulb (one for tail, one for brake) or a single filament bulb for tail light only. Look for a broken filament within the bulb. If the bulb appears physically intact, gently remove it and check its base and socket for corrosion or damage.
3. Fuse Check: Consult the vehicle's owner's manual or fuse box diagram (usually located in the engine bay or under the dashboard) to identify the fuse for the "Tail Lights" or "Parking Lights." Carefully pull the identified fuse. Visually inspect the fuse for a broken filament. If it's a blade fuse, check the metal strip.
Using a Multimeter: Set to continuity mode. Touch probes to both metal terminals of the fuse. A beep or a reading of 0 ohms indicates a good fuse. No beep or an "OL" (open loop) reading indicates a blown fuse.
Outcome: If the fuse is blown, replace it with a new one of the correct ampere rating. If the new fuse blows immediately, there's a short circuit in the wiring.
4. Voltage Check at Bulb Socket: If the bulb and fuse are good, or if the fuse was blown and replaced but the light still doesn't work (and the new fuse didn't blow), reinstall a known good bulb. With the parking lights ON, use a multimeter set to DC Volts. Locate the tail light terminal in the bulb socket. Place the positive probe there. Place the negative probe on a clean, unpainted metal part of the vehicle chassis (good ground).
Expected Reading: Approximately 12
V. Interpretation: If 12V is present, but the bulb doesn't light up (and the bulb is confirmed good), the issue is a poor ground connection at the bulb socket or within the assembly. If 0V, there's an open circuit between the fuse box and the bulb socket (e.g., broken wire, faulty switch, or relay upstream).
5. Ground Check at Bulb Socket: If voltage was present but no light, turn off the ignition. Set the multimeter to continuity mode. Place one probe on the ground terminal of the bulb socket and the other on a known good chassis ground.
Expected Reading: A beep or near 0 ohms.
Interpretation: If "OL" or high resistance, the ground connection is faulty. Clean corrosion, tighten connections, or trace the ground wire for breaks.
Conclusion for Scenario: In this specific scenario, since only the tail light is out and the brake/turn signals are fine, the most likely immediate causes are a blown tail light filament in a dual-filament bulb, a faulty single-filament tail light bulb, or a specific loose connection to the tail light terminal in the socket. A specific fuse for the tail light circuit would also be a strong candidate. 2.
3. Replacing Bulbs and Fuses (Performance Objective 2)
Safety Precautions: * Always switch off the ignition and turn The automotive lighting system comprises various electrical components working in unison to provide illumination for the driver, signal intentions to other road users, and illuminate the vehicle's interior. 2.
1. Components of the Lighting System: Bulbs: Convert electrical energy into light. Different types include incandescent, halogen, LED (Light Emitting Diode), and HID (High-Intensity Discharge).
Headlamps: Provide forward illumination.
Tail Lamps/Rear Lights: Red lights at the rear, visible to following vehicles.
Brake Lights/Stop Lamps: Brighter red lights at the rear, activated when brakes are applied.
Turn Signal Lamps/Indicators: Amber lights at the front, side, and rear, indicating turns or lane changes.
Parking Lamps: Low-intensity lights (front and rear) for parking or being visible when stationary.
Reverse Lamps: White lights at the rear, activated when reverse gear is engaged.
Fog Lamps: Auxiliary lamps for improved visibility in foggy conditions.
Instrument Panel/Dashboard Lights: Illuminate gauges and controls.
Interior/Dome Lights: For cabin illumination.
Fuses: Protective devices that melt and break a circuit when current exceeds a safe level, preventing damage to wiring and components. Common types in Nigeria are blade fuses (ATO, Mini, Maxi) and glass tube fuses.
Switches: Control the flow of electricity to different lighting circuits (e.g., headlamp switch, turn signal switch, brake pedal switch).
Relays: Electromechanical switches that use a small current to control a larger current, often used in headlamp circuits due to high current draw.
Wiring Harness: Connects all components, carrying electrical current.
Battery: Provides the primary power source.
Alternator: Recharges the battery and supplies power when the engine is running. 2.
2. Locating Faults in the Lighting System (Performance Objective 1) Troubleshooting electrical faults requires a systematic approach.
Common faults include: Open Circuit: A break in the electrical path, preventing current flow.
Causes: blown fuse, faulty bulb filament, broken wire, loose connection, faulty switch/relay.
Short Circuit: An unintended path for current to flow, bypassing resistance, often resulting in excessive current and a blown fuse.
Causes: worn insulation allowing wires to touch, wire touching vehicle chassis.
High Resistance: Increased resistance in a circuit due to corrosion, loose connections, or damaged wiring, leading to dim lights or intermittent operation.
Faulty Component: A bulb, switch, or relay itself is defective.
Troubleshooting Procedure:
1. Symptom Verification: Confirm the specific light(s) not working. (e.g., "Right headlamp is out," "No brake lights").
2. Visual Inspection: Check the affected bulb(s) for a broken filament or discolouration. Inspect wiring for visible damage, cuts, or burnt sections. Check for loose or corroded connections at the bulb sockets, switch terminals, and fuse box.
Inspect the fuse box: Look for a blown fuse associated with the faulty circuit. A blown fuse will have a visible break in its metal strip or filament.
3. Basic Electrical Checks (Using a Multimeter or Test Light): Fuse Check (Continuity): Remove the suspected fuse. Use a multimeter set to continuity mode (or resistance mode, looking for near zero ohms) to check if the fuse is intact. A test light will illuminate if the fuse is good when connected across its terminals (after removing it from the circuit and applying power via a battery).
Voltage Check (Power Supply): With the ignition ON and the relevant light switch activated, use a multimeter (set to DC Volts) to check for voltage at the bulb socket. Place the positive probe at the positive terminal of the bulb socket and the negative probe on a good chassis ground. A reading close to battery voltage (12-14V) indicates power supply is reaching the socket. No voltage indicates an open circuit upstream.
Ground Check (Continuity): Use a multimeter (continuity or resistance mode) to check for a good ground connection at the bulb socket. Place one probe on the ground terminal of the socket and the other on a known good chassis ground. A reading of near zero ohms indicates a good ground. High resistance or open circuit indicates a bad ground.
Switch/Relay Check: Check for voltage input and output at the switch or relay terminals to determine if they are functioning correctly. *Worked Example for Fault trace the ground wire for breaks.
Conclusion for Scenario: In this specific scenario, since only the tail light is out and the brake/turn signals are fine, the most likely immediate causes are a blown tail light filament in a dual-filament bulb, a faulty single-filament tail light bulb, or a specific loose connection to the tail light terminal in the socket. A specific fuse for the tail light circuit would also be a strong candidate. 2.
3. Replacing Bulbs and Fuses (Performance Objective 2)
Safety Precautions: Always switch off the ignition and turn off all lights before working on the lighting system. Disconnect the vehicle's negative battery terminal to prevent accidental short circuits, especially when working on major components or if there's any doubt about exposed wires. Allow bulbs, especially headlamps, to cool down before handling, as they can be very hot. When handling halogen bulbs, avoid touching the glass part directly with bare hands, as skin oils can create hot spots and reduce bulb life. Use clean gloves or a cloth. Always use bulbs and fuses with the correct specifications (voltage, wattage, ampere rating) as specified by the vehicle manufacturer. Procedure for Replacing a Bulb (e.g., Headlamp/Parking Lamp):
1. Access: Open the bonnet for headlamps, or remove the tail light/parking light assembly cover from the inside of the boot or fender. Some parking lamps require accessing from behind the headlight assembly.
2. Disconnect Power: Ensure the light switch is OF
F. Disconnecting the battery is advisable for major work.
3. Remove Electrical Connector: Gently twist or pull the electrical connector from the back of the bulb or bulb holder.
4. Remove Retaining Mechanism: Headlamps (Halogen): May involve a spring clip, a plastic collar, or a screw-in mechanism. Carefully release or unscrew it. Smaller Bulbs (e.g., Parking, Tail, Turn Signal): The bulb is usually housed in a twist-lock or push-in socket. Twist the socket (typically counter-clockwise) to remove it from the lamp housing, then pull the bulb straight out or twist it.
5. Remove Old Bulb: Pull the bulb straight out or twist it counter-clockwise (for bayonet-style bulbs).
6. Install New Bulb: Align the new bulb with the socket/housing. For halogen headlamps, ensure the tabs align correctly. For bayonet bulbs, push in and twist clockwise. For wedge bulbs, simply push in.
Crucial: Do NOT touch the glass of halogen headlamps with bare hands.
7. Secure Retaining Mechanism: Reinstall the spring clip, collar, or screw mechanism.
8. Reconnect Electrical Connector: Push or twist the electrical connector back onto the bulb or socket until it clicks securely.
9. Test: Connect the battery (if disconnected), turn on the ignition, and test the new bulb's functionality.
1
0. Reassemble: Replace any covers or trim panels.
Procedure for Replacing a Fuse:
1. Locate Fuse Box: Refer to the owner's manual for the location(s) of the fuse box (typically under the dashboard, in the engine compartment, or in the boot).
2. Identify Blown Fuse: Consult the fuse box diagram (usually inside the fuse box cover) to locate the specific fuse for the faulty circuit. Visually inspect the fuse. A blown blade fuse will have a broken metal strip; a blown glass fuse will have a broken internal wire. Alternatively, use a fuse puller (often found in the fuse box cover) to remove suspected fuses one by one and check for continuity with a multimeter.
3. Remove Blown Fuse: Use a fuse puller or small pliers to carefully pull the blown fuse straight out.
4. Install New Fuse: Crucial: Always replace a blown fuse with a new one of the exact same ampere (A) rating. Using a higher-rated fuse can cause severe electrical damage or fire; a lower-rated fuse will blow prematurely. Push the new fuse firmly into its slot.
5. Test: Turn on the ignition and test the affected electrical component. If the new fuse blows immediately, there is a short circuit in the wiring that needs to be located and repaired before installing another fuse.
6. Replace Cover: Close the fuse box cover securely. 2.
4. Aligning Headlamps (Performance Objective 3) Proper headlamp alignment is crucial for road of the exact same ampere (A) rating. Using a higher-rated fuse can cause severe electrical damage or fire; a lower-rated fuse will blow prematurely. Push the new fuse firmly into its slot.
5. Test: Turn on the ignition and test the affected electrical component. If the new fuse blows immediately, there is a short circuit in the wiring that needs to be located and repaired before installing another fuse.
6. Replace Cover: Close the fuse box cover securely. 2.
4. Aligning Headlamps (Performance Objective 3) Proper headlamp alignment is crucial for road safety. Misaligned headlamps can blind oncoming drivers (if aimed too high) or provide insufficient illumination of the road ahead (if aimed too low or off to the side).
Tools Required: Measuring tape Marker pen or chalk Phillips screwdriver or appropriate wrench (depending on vehicle adjustment screws) A clean, flat wall or garage door A level ground for the vehicle. Procedure for Headlamp Alignment (Static/Wall Screen Method):
1. Preparation: Park the vehicle on a level surface, perpendicular to a flat wall. Ensure tyre pressures are correct and consistent. The vehicle should have a normal load (e.g., driver only or a typical passenger load, not excessively heavy in the boot). The fuel tank should be at least half full. Clean the headlamp lenses.
Crucial: Measure the distance from the headlamp lens to the wall. For this practical method, 25 feet (approximately 7.6 meters) is a common standard, though some manufacturers specify 10 feet (3 meters) or 30 feet (9.1 meters). Let's use 25 feet for this example, as it provides a good working distance.
2. Mark Reference Lines on the Wall: Centre Line: Measure the exact centre of the vehicle (e.g., centre of the grille or windscreen) and mark a vertical line on the wall corresponding to this.
Headlamp Centre Lines: Measure the distance from the vehicle's centre to the centre of each headlamp. Mark two vertical lines on the wall, one for each headlamp, matching these distances on either side of the vehicle's centre line.
Horizontal Line (H-Line): Measure the height from the ground to the centre of each headlamp lens. Mark a horizontal line on the wall at this exact height.
Cut-off Line (Adjustment Line): For low beams, the top of the beam's intense part should typically be 2 inches (5 cm) below the H-line for standard alignment. Mark a new horizontal line 2 inches below the H-line. This is your target for the top of the low beam pattern.
3. Adjust Headlamps: Turn on the low beam headlamps. Cover one headlamp with a thick cloth or cardboard to prevent its light from interfering while adjusting the other.
Vertical Adjustment: Locate the vertical adjustment screw or knob on the headlamp assembly (usually behind or above the headlamp). Turn it to move the headlamp beam up or down. Aim the sharp horizontal cut-off of the low beam pattern so its top edge aligns with the cut-off line (2 inches below the H-line) on the wall.
Horizontal Adjustment: Locate the horizontal adjustment screw or knob. Turn it to move the headlamp beam left or right. Aim the most intense part of the beam (often a "hot spot" or a slight upward kick) to be directly on or slightly to the right (for right-hand drive vehicles, or slightly to the left for left-hand drive vehicles common in Nigeria) of the corresponding headlamp centre vertical line. This allows for better illumination of the roadside. A common guide is to have the 'kick-up' or inner edge of the beam pattern align with the vertical centre of its respective headlamp. Repeat the process for the other headlamp.
4. Final Check: Uncover both headlamps. Visually inspect the beam patterns on the wall. They should be symmetrical and correctly aligned with your target lines. Take the vehicle for a short drive in a safe area to confirm the alignment feels correct and does not blind oncoming drivers.
Note: For vehicles with high beams, ensure they are also aligned appropriately. High beams are typically aimed higher
Road Safety and Accident Prevention: Application: In Nigeria, poorly maintained vehicle lighting is a significant contributor to road accidents, especially at night or in adverse weather (e.g., heavy rains common during rainy seasons). Properly functioning headlamps ensure the driver can see hazards (potholes, livestock, pedestrians) and other vehicles, while functional tail lights, brake lights, and turn signals communicate the driver's intentions to others, preventing rear-end collisions or side-swipes in busy traffic (e.g., Lagos-Ibadan Expressway).
Integration: Students can be tasked with inspecting vehicles in their community (family cars, Keke Napeps, Okada) for lighting defects and suggesting necessary repairs, relating their learning directly to improving local road safety. Automotive Entrepreneurship and Job Creation: Application: The skills learned in diagnosing and repairing lighting systems (replacing bulbs, fuses, aligning headlamps) are highly sought after in Nigeria's informal and formal automotive sectors. Many drivers rely on roadside mechanics (mechanic villages) for quick fixes. A skilled technician can establish a reputable business specializing in electrical diagnostics and lighting repairs.
Integration: Discuss with students how they can market these specific skills. For instance, creating a business plan for a "Mobile Lighting System Repair" service that serves private car owners, taxi drivers, and commercial bus operators in their local area, highlighting the potential for income generation. Vehicle Roadworthiness and Regulatory Compliance: Application: Vehicle Inspection Officers (VIOs) and the Federal Road Safety Corps (FRSC) in Nigeria conduct routine checks for vehicle roadworthiness. Defective lighting systems (e.g., one-eyed vehicles, non-functional brake lights) are common reasons for fines, vehicle impoundment, or failure during inspection. Knowing how to maintain and repair these systems ensures compliance.
Integration: Students can research the specific FRSC regulations regarding vehicle lighting in Nigeria. They can then conduct a mock VIO inspection on a school vehicle or a local vehicle, identifying non-compliance issues related to lighting and explaining how to rectify them to meet regulatory standards.