I85PREP
⌘ K
NITA Auto Electrician Trade Test study materials
NITA Auto Electrician Trade Test study resources

NITA Auto Electrician Trade Test practice questions

One question at a time. Build your NITA Auto Electrician Trade Test understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Electrical Principles and Circuit Fundamentals

In a 12 V auto electrical system, a headlamp circuit draws 8 A through the switch and wiring. What is the total resistance of that circuit under normal operation?

  1. 96 Ω
  2. 0.67 Ω
  3. 1.5 kΩ
  4. 1.5 Ω Correct answer.

Explanation

Ohm's law gives R = V ÷ I, so 12 V divided by 8 A equals 1.5 Ω. This is the effective resistance of lamp filament plus wiring and switch contacts combined.

Question 2Electrical Principles and Circuit Fundamentals

Two 12 V lamps are connected in parallel across the battery. Which statement describes the voltage across each lamp?

  1. The voltages divide equally, so each lamp sees 6 V.
  2. The voltage across each lamp depends on its filament colour.
  3. Each lamp sees approximately the full battery voltage. Correct answer.
  4. The first lamp sees full voltage and the second sees less.

Explanation

In a parallel circuit every branch is connected directly across the supply, so each branch sees the same source voltage. Branch current then depends on each lamp's own resistance.

Question 3Electrical Principles and Circuit Fundamentals

A starter motor draws a very large current from the battery. What is the main reason heavy-gauge cable is specified for the starter circuit?

  1. To reduce the inductance of the motor windings
  2. To raise the battery open-circuit voltage
  3. To limit voltage drop caused by cable resistance at high current Correct answer.
  4. To increase the circuit resistance and protect the motor

Explanation

Voltage drop equals current multiplied by cable resistance, so a large starter current through thin cable would waste supply voltage as heat. Thick conductors lower resistance and keep most of the battery voltage at the motor.

Question 4Electrical Principles and Circuit Fundamentals

A 55 W halogen headlamp bulb operates at its rated 12 V. What current does it draw?

  1. 0.22 A
  2. 660 A
  3. 4.6 A Correct answer.
  4. 55 A

Explanation

Power equals voltage multiplied by current, so current equals power divided by voltage. Dividing 55 W by 12 V gives about 4.6 A.

Question 5Electrical Principles and Circuit Fundamentals

Which material is used for the conductor core of automotive battery cables because of its low resistivity?

  1. Copper Correct answer.
  2. Rubber
  3. Aluminium oxide
  4. Carbon

Explanation

Copper has very low resistivity and good mechanical ductility, making it the standard conductor in automotive cable. Its low resistance keeps voltage drop small in high-current circuits.

Question 6Electrical Principles and Circuit Fundamentals

What is the conventional direction of current flow in an automotive circuit diagram?

  1. From the positive terminal, through the load, to the negative terminal Correct answer.
  2. Alternating back and forth at the alternator's rotational speed
  3. From the negative terminal, through the load, to the positive terminal
  4. From the alternator to the battery only, never through loads

Explanation

Conventional current is defined as flowing from the positive terminal through the external circuit to the negative terminal. Electron flow is in the opposite direction, but circuit diagrams and most service literature use the conventional convention.

Question 7Electrical Principles and Circuit Fundamentals

A 12 V circuit has three resistors of 4 Ω, 6 Ω and 8 Ω connected in series. What is the total circuit resistance?

  1. 18 Ω Correct answer.
  2. 2.2 Ω
  3. 1.8 Ω
  4. 0.55 Ω

Explanation

In a series circuit resistances add directly, so 4 plus 6 plus 8 equals 18 Ω. The same current flows through every element and the supply voltage divides across them.

Question 8Electrical Principles and Circuit Fundamentals

A 12 V supply is connected across resistors of 6 Ω and 3 Ω in parallel. What total current flows from the supply?

  1. 1.33 A
  2. 4 A
  3. 0.67 A
  4. 6 A Correct answer.

Explanation

The parallel equivalent resistance is 2 Ω, found from the reciprocal sum of 1/6 and 1/3. Using I = V ÷ R gives 12 V divided by 2 Ω, which is 6 A.

Question 9Electrical Principles and Circuit Fundamentals

A relay coil rated at 12 V and 120 Ω is to be driven from a 12 V supply. Which coil current should the control circuit be able to switch?

  1. 0.01 A
  2. 10 A
  3. 1.44 A
  4. 0.1 A Correct answer.

Explanation

Ohm's law gives coil current as 12 V divided by 120 Ω, which is 0.1 A. The driver transistor or switch must handle at least this current plus a margin.

Question 10Electrical Principles and Circuit Fundamentals

A technician measures 10.5 V at the battery posts while the engine is cranking. Which conclusion is most reasonable?

  1. The starter motor has open-circuit windings.
  2. The battery is fully charged and the meter is faulty.
  3. The alternator is overcharging the battery during cranking.
  4. The battery is heavily loaded and its internal resistance is causing a significant drop. Correct answer.

Explanation

A healthy battery typically holds well above 10.5 V under cranking load; a large drop indicates high internal resistance or a discharged battery. The reading reflects the source voltage sagging under high starter current.

Question 11Electrical Principles and Circuit Fundamentals

An ammeter is to be used to measure current through a fuel pump circuit. How should it be connected?

  1. In series with the pump, with the circuit broken to insert the meter Correct answer.
  2. In parallel across the battery terminals
  3. Between the pump body and chassis earth
  4. In parallel across the pump terminals

Explanation

An ammeter has very low internal resistance and must carry the circuit current, so it is connected in series. The circuit is opened and the meter inserted so that all pump current passes through it.

Question 12Electrical Principles and Circuit Fundamentals

A voltmeter reads 12.6 V at the battery but only 9.8 V at the headlamp connector with the lamps on. Which fault is most consistent with these readings?

  1. A short circuit across the headlamp bulb
  2. High resistance in the supply wiring or switch contacts Correct answer.
  3. An open circuit in the headlamp earth return
  4. A failed voltage regulator in the alternator

Explanation

A voltage difference of about 2.8 V between source and load indicates excessive voltage drop along the supply path. Corroded terminals, undersized cable or burned switch contacts raise resistance and dissipate power before it reaches the lamp.

Question 13Electrical Principles and Circuit Fundamentals

A 12 V circuit contains a 4 Ω resistor in series with two 8 Ω resistors in parallel. What is the total resistance?

  1. 20 Ω
  2. 8 Ω Correct answer.
  3. 2.67 Ω
  4. 6 Ω

Explanation

Two 8 Ω resistors in parallel give 4 Ω; adding the series 4 Ω resistor gives 8 Ω total. Series and parallel rules are applied in stages.

Question 14Electrical Principles and Circuit Fundamentals

Which statement correctly distinguishes electrical power from electrical energy in an auto electrical context?

  1. Power and energy are the same quantity measured in different units.
  2. Power is the rate of energy transfer in watts, while energy is power multiplied by time. Correct answer.
  3. Power is stored in the battery, while energy flows only through the alternator.
  4. Power is measured in ampere-hours and energy in watts.

Explanation

Power describes how quickly energy is transferred and is measured in watts, equal to volts times amperes. Energy is the accumulated quantity, so a battery's ampere-hour rating multiplied by voltage gives watt-hours of stored energy.

Question 15Electrical Principles and Circuit Fundamentals

A fuse protecting a 12 V circuit rated at 10 A continuous is being selected. Why is a fuse slightly above the continuous current chosen rather than one exactly at 10 A?

  1. Because fuses only protect against overvoltage
  2. To avoid nuisance blowing from inrush and normal current tolerance while still protecting the cable Correct answer.
  3. To allow the circuit to carry unlimited current during faults
  4. Because a lower-rated fuse would increase circuit voltage

Explanation

Motors and lamps draw brief inrush currents above their running value, and fuses have tolerance, so a margin prevents nuisance operation. The rating is still chosen to protect the cable from sustained overload.

Question 16Electrical Principles and Circuit Fundamentals

A technician needs to identify whether a parasitic drain is present on a parked vehicle. Which measurement approach is appropriate?

  1. Measure current flow from the battery with all loads off and modules allowed to sleep Correct answer.
  2. Measure voltage across the battery with the engine running
  3. Measure resistance across the battery terminals with the battery connected
  4. Measure current with the starter engaged

Explanation

Parasitic drain is a small current that continues to flow after modules enter sleep mode, so it is measured in series with the battery. Voltage or resistance checks with the battery connected do not reveal the drain magnitude.

Question 17Electrical Principles and Circuit Fundamentals

A wire of the same material and length has twice the cross-sectional area of another. How does its resistance compare?

  1. It is twice the resistance of the thinner wire.
  2. It is four times the resistance of the thinner wire.
  3. It is half the resistance of the thinner wire. Correct answer.
  4. It is unchanged because length is the same.

Explanation

Resistance is inversely proportional to cross-sectional area for a given material and length. Doubling the area halves the resistance, which is why thicker cable carries more current with less drop.

Question 18Electrical Principles and Circuit Fundamentals

A 24 V truck circuit has a 6 Ω load and a 2 Ω cable-and-connector resistance in series. What power is dissipated in the cable and connectors?

  1. 9 W
  2. 72 W
  3. 18 W Correct answer.
  4. 36 W

Explanation

Total resistance is 8 Ω, so circuit current is 24 V divided by 8 Ω, which is 3 A. Cable power is I squared times R, giving 9 times 2, or 18 W lost as heat.

Question 19Electrical Principles and Circuit Fundamentals

A circuit has a 12 V source feeding a 3 Ω load through wiring of 1 Ω total. By what percentage does the load voltage fall short of the source voltage?

  1. 10 percent
  2. 75 percent
  3. 33 percent
  4. 25 percent Correct answer.

Explanation

Total resistance is 4 Ω, so current is 3 A and the wiring drops 3 V, leaving 9 V at the load. The 3 V drop is one quarter of 12 V, a 25 percent shortfall.

Question 20Electrical Principles and Circuit Fundamentals

An ignition coil primary is switched on and off rapidly. Why does a capacitor or suppression diode across the switching contacts matter for circuit protection?

  1. The capacitor stores charge to keep the coil energised after the engine stops.
  2. The diode converts the coil's DC supply into AC for the spark plugs.
  3. The collapsing magnetic field induces a high voltage that would otherwise arc across and erode the contacts. Correct answer.
  4. The capacitor increases the primary current to strengthen the spark.

Explanation

When primary current is interrupted, the coil's inductance produces a large induced EMF that can arc across the switch and burn the contacts. A capacitor or clamping diode provides a path that limits this voltage spike.

Question 21Batteries, Charging and Starting Systems

A 12 V lead-acid battery has six cells connected in series. What is the nominal voltage of each cell?

  1. 2.4 V
  2. 2.1 V Correct answer.
  3. 6.0 V
  4. 1.5 V

Explanation

A lead-acid cell produces about 2.1 V nominal when fully charged, and six cells in series give the familiar 12.6 V open-circuit reading. This is why a healthy 12 V battery rests slightly above 12 V rather than exactly at 12 V.

Question 22Batteries, Charging and Starting Systems

What is the main function of the battery in a vehicle starting system?

  1. To supply high current to the starter motor and stabilise system voltage Correct answer.
  2. To step down alternator output for the lighting circuit
  3. To convert mechanical energy into electrical energy while driving
  4. To filter radio interference from the ignition circuit

Explanation

The battery stores chemical energy and delivers the very high cranking current the starter needs, while also acting as a voltage buffer for the rest of the electrical system. Energy conversion while driving is the alternator's job, not the battery's.

Question 23Batteries, Charging and Starting Systems

Which component prevents the battery from discharging back through the alternator when the engine is stopped?

  1. The ignition switch
  2. The rectifier diodes Correct answer.
  3. The field winding
  4. The voltage regulator

Explanation

The rectifier diodes in the alternator act as one-way valves, so current can flow from the alternator to the battery but not back through the stator windings when the engine stops. Without them the battery would drain through the alternator.

Question 24Batteries, Charging and Starting Systems

A customer reports the engine cranks slowly and the headlights dim when the starter is engaged. Which test should be performed first?

  1. A compression test on all cylinders
  2. A fuel pressure test
  3. A battery state-of-charge and load test Correct answer.
  4. An alternator ripple voltage test

Explanation

Slow cranking with dimming lights points to a weak battery or high-resistance starting circuit, so battery state of charge and load capacity should be checked first. Compression, ripple and fuel pressure tests are secondary until the battery is proven good.

Question 25Batteries, Charging and Starting Systems

What is the purpose of the alternator's voltage regulator?

  1. To convert AC to DC in the rectifier bridge
  2. To disconnect the battery during over-revving
  3. To hold charging voltage within a set range by controlling field current Correct answer.
  4. To limit starter current during cranking

Explanation

The regulator varies field current so that alternator output stays near the specified charging voltage regardless of engine speed and load. This protects the battery from overcharging and keeps electrical systems supplied.

Question 26Batteries, Charging and Starting Systems

Which electrolyte is used in a conventional lead-acid automotive battery?

  1. Potassium hydroxide solution
  2. Sodium chloride solution
  3. Phosphoric acid solution
  4. Sulphuric acid diluted with distilled water Correct answer.

Explanation

Lead-acid batteries use dilute sulphuric acid as the electrolyte, which reacts with the lead and lead dioxide plates during charge and discharge. Potassium hydroxide is used in nickel-cadmium cells, not lead-acid.

Question 27Batteries, Charging and Starting Systems

A technician sees a white, crusty deposit around a battery terminal. What is this deposit and how should it be treated?

  1. Electrolyte gel, left in place to seal the terminal
  2. Copper oxide, removed by sanding the post
  3. Lead sulphate, removed by adding acid to the terminal
  4. Corrosion, cleaned off with a bicarbonate solution and a terminal brush Correct answer.

Explanation

The white crust is corrosion formed when acid vapours attack the terminal, and it is neutralised with a baking-soda solution before being brushed clean. Leaving it in place increases resistance and causes charging and cranking faults.

Question 28Batteries, Charging and Starting Systems

What does the cold cranking ampere (CCA) rating of a battery indicate?

  1. The current it can deliver for 20 hours at 25 degrees C
  2. The total energy stored in ampere-hours at 20 degrees C
  3. The current it can deliver for 30 seconds at -18 degrees C while staying above 7.2 V Correct answer.
  4. The maximum charging current the alternator may supply

Explanation

CCA rates a battery's ability to crank a cold engine: the discharge current sustained for 30 seconds at -18 degrees C without falling below 7.2 V. This is the figure that matters when selecting a battery for cold climates.

Question 29Batteries, Charging and Starting Systems

During a charging system test the alternator output measures 13.2 V at 2000 rpm with all accessories on. What is the most likely cause?

  1. A worn alternator drive belt slipping under load Correct answer.
  2. An open field winding
  3. A battery with a high CCA rating
  4. A shorted rectifier diode

Explanation

A low but present output that worsens under load often indicates belt slip, since the alternator cannot spin fast enough to meet demand. Diode or field faults usually give a larger drop or no output at all.

Question 30Batteries, Charging and Starting Systems

A battery is being charged at 10 A for 5 hours. How much charge has been put into it?

  1. 2 Ah
  2. 15 Ah
  3. 50 Ah Correct answer.
  4. 500 Ah

Explanation

Charge in ampere-hours equals current multiplied by time, so 10 A for 5 hours gives 50 Ah. This simple calculation is used to estimate recharge time and capacity restored.

Question 31Batteries, Charging and Starting Systems

Which test best reveals a battery that has good open-circuit voltage but cannot deliver cranking current?

  1. An open-circuit voltage check
  2. A charging system ripple test
  3. A specific gravity check on one cell
  4. A high-rate discharge or load test Correct answer.

Explanation

A load test applies a high current and measures how well the battery holds voltage, exposing a battery that looks fine at rest but collapses under cranking demand. Open-circuit voltage alone cannot reveal lost cranking capacity.

Question 32Batteries, Charging and Starting Systems

What is the effect of connecting two identical 12 V batteries in parallel?

  1. The voltage halves to 6 V and the capacity doubles
  2. The voltage stays at 12 V and the available capacity doubles Correct answer.
  3. The voltage stays at 12 V and the capacity halves
  4. The voltage doubles to 24 V and the capacity stays the same

Explanation

In a parallel connection the positive terminals are joined together and the negative terminals together, so voltage remains the same while the combined ampere-hour capacity adds up. Series connection, by contrast, adds voltage.

Question 33Batteries, Charging and Starting Systems

A starter motor solenoid clicks repeatedly but the motor does not turn. Which fault is most consistent with this symptom?

  1. Insufficient current through a high-resistance battery cable Correct answer.
  2. A blown headlamp fuse
  3. An open circuit in the alternator field
  4. A seized starter pinion gear

Explanation

Rapid clicking usually means the solenoid engages but the voltage collapses as soon as the heavy current is drawn, which points to high resistance in the cables or a discharged battery. A seized pinion would produce a single heavy clunk or a stalled motor.

Question 34Batteries, Charging and Starting Systems

What is the purpose of the overrunning clutch in a starter drive?

  1. To hold the pinion engaged while cranking
  2. To connect the solenoid to the ignition switch
  3. To let the pinion spin freely once the engine starts Correct answer.
  4. To increase the gear reduction ratio

Explanation

Once the engine fires it spins faster than the starter, so the overrunning clutch allows the pinion to freewheel and prevents the engine from driving the starter armature at damaging speed. It releases rather than locks in that direction.

Question 35Batteries, Charging and Starting Systems

A vehicle's charging voltage rises to 15.8 V at cruising speed. What is the likely consequence if left uncorrected?

  1. The alternator will stop charging entirely
  2. The battery will overcharge and its electrolyte will be lost through gassing Correct answer.
  3. The headlamps will be dim at idle
  4. The starter will crank too slowly

Explanation

Excessive charging voltage drives the battery into heavy gassing, boiling off electrolyte and shortening its life. It can also damage bulbs and electronic modules, so the regulator or its sense circuit must be checked.

Question 36Batteries, Charging and Starting Systems

Which condition indicates that a lead-acid battery is fully charged when checked with a hydrometer?

  1. All cells read about 1.120 specific gravity
  2. All cells read about 1.265 specific gravity and are within 0.050 of each other Correct answer.
  3. All cells read about 1.000 specific gravity
  4. One cell reads 1.265 and the rest read 1.150

Explanation

A fully charged lead-acid cell reads roughly 1.265 specific gravity, and all cells should be close to each other. A large spread between cells indicates a failing cell.

Question 37Batteries, Charging and Starting Systems

What is the function of the commutator in a conventional starter motor?

  1. To reverse the current in the armature windings as the armature rotates Correct answer.
  2. To engage the pinion with the flywheel
  3. To hold the brushes against the field coils
  4. To reduce the speed of the armature

Explanation

The commutator and brushes switch the current direction in the armature coils at the right moment so that torque is produced continuously. It is a current-reversing device, not a speed-reduction or engagement mechanism.

Question 38Batteries, Charging and Starting Systems

A technician needs to test for excessive voltage drop in the starter's earth circuit. Where should the voltmeter leads be connected?

  1. Between the alternator B+ terminal and the battery positive post, with the engine running
  2. Between the solenoid trigger terminal and earth, with the ignition on
  3. Between the battery negative post and the starter housing, while cranking Correct answer.
  4. Between the battery positive and negative posts, with the engine off

Explanation

Voltage drop testing places the meter across the path being tested, so for the earth side the leads go from the battery negative post to the starter housing while the circuit is loaded by cranking. A reading above roughly 0.2 V indicates excessive resistance.

Question 39Batteries, Charging and Starting Systems

Which statement correctly describes the difference between a battery's reserve capacity and its ampere-hour rating?

  1. Reserve capacity is the minutes it can supply a fixed load, while ampere-hours express total charge capacity Correct answer.
  2. Reserve capacity applies only to 24 V systems, while ampere-hours apply to 12 V systems
  3. Reserve capacity measures cold cranking, while ampere-hours measure charging voltage
  4. Reserve capacity is measured in amperes, while ampere-hours are measured in minutes

Explanation

Reserve capacity is expressed in minutes and describes how long the battery can keep essential loads running if the alternator fails. Ampere-hours express the total charge the battery can deliver and are a different measure entirely.

Question 40Batteries, Charging and Starting Systems

A customer's battery keeps going flat overnight despite a healthy alternator and battery. Which procedure is appropriate?

  1. Top up the electrolyte with acid
  2. Measure parasitic current draw with an ammeter in series after all modules have gone to sleep Correct answer.
  3. Increase the alternator belt tension
  4. Replace the voltage regulator

Explanation

A repeated overnight discharge with good charging points to a parasitic drain, so current draw should be measured in series once the vehicle's modules have entered sleep mode. This isolates the offending circuit.

Question 41Batteries, Charging and Starting Systems

Why must a battery be disconnected negative terminal first during service work?

  1. To prevent a short circuit through the spanner to the vehicle body Correct answer.
  2. To allow the alternator to discharge safely
  3. To avoid damaging the positive terminal threads
  4. To reset the engine control module

Explanation

The negative terminal is connected to the vehicle body, so removing it first means a spanner touching the body cannot complete a circuit. Removing the positive first risks a dead short if the tool contacts earthed metal.

Question 42Batteries, Charging and Starting Systems

An alternator is bench tested and produces good output, but on the vehicle it charges poorly at idle and improves with revs. Which cause best fits this pattern?

  1. The rectifier bridge has failed open
  2. The alternator is undersized or the belt ratio is wrong for idle speed Correct answer.
  3. The battery has a shorted cell
  4. The starter solenoid is drawing current

Explanation

Output rising with engine speed suggests the alternator cannot produce enough at idle, often because it is undersized or the pulley ratio is wrong. A failed rectifier would reduce output at all speeds.

Question 43Batteries, Charging and Starting Systems

A 12 V system is fitted with an alternator whose warning lamp stays illuminated with the engine running and charging voltage is normal. Which fault is most likely?

  1. An open circuit in the lamp's control or sense circuit Correct answer.
  2. A slipping drive belt
  3. A failed main rectifier diode
  4. A discharged battery

Explanation

If charging voltage is normal, the alternator itself is working and the lamp is being lit by a fault in its own control or sense circuit. Diode or belt faults would normally depress charging voltage.

Question 44Batteries, Charging and Starting Systems

Two 12 V batteries in series feed a 24 V starter circuit. One battery is weak and collapses under load. What is the effect on the circuit?

  1. Total voltage falls sharply and the starter turns slowly or not at all Correct answer.
  2. Total voltage stays at 24 V because the good battery compensates
  3. The good battery overcharges the weak one during cranking
  4. The weak battery reverses its polarity and boosts the circuit

Explanation

In a series circuit the same current flows through both batteries, so the weakest one limits performance and its voltage collapse reduces total available voltage. The strong battery cannot compensate for the weak one.

Question 45Batteries, Charging and Starting Systems

A starter motor draws excessive current and turns slowly even with a fully charged battery and clean cables. Which internal fault is most likely?

  1. A faulty ignition switch
  2. A short circuit between armature windings or an earthed field coil Correct answer.
  3. A worn brush spring
  4. An open armature winding

Explanation

Excessive current with slow rotation indicates low internal resistance, typically a shorted armature or an earthed field winding. An open winding would instead give no current and no rotation.

Question 46Batteries, Charging and Starting Systems

During a charging system check on a 12 V vehicle, the technician measures 14.4 V at the battery terminals with the engine at fast idle and no accessories on. Which conclusion is correct?

  1. The alternator output is within the normal charging voltage range. Correct answer.
  2. The regulator is faulty because the voltage is too high for a 12 V battery.
  3. The alternator is not charging because voltage must exceed 15 V.
  4. The battery is overcharged and will gas violently at this voltage.

Explanation

A healthy 12 V charging system typically regulates between about 13.8 V and 14.7 V at the battery terminals, so 14.4 V sits comfortably inside the normal band. This reading shows the alternator is supplying charge current and the regulator is controlling the field correctly.

Question 47Batteries, Charging and Starting Systems

A maintenance-free battery has a built-in hydrometer eye that shows dark. What does this indication mean?

  1. The battery has an internal open circuit and must be replaced immediately.
  2. The battery is fully charged and needs no further checks.
  3. The electrolyte level or state of charge requires further testing with a voltmeter or load tester. Correct answer.
  4. The battery is overfilled with electrolyte and will overflow.

Explanation

A dark or green eye generally indicates only that the electrolyte density has fallen below the float's reference point, which can result from low charge or low electrolyte. It is a rough indicator, so the battery must still be confirmed with an open-circuit voltage measurement and a load or conductance test.

Question 48Batteries, Charging and Starting Systems

While cranking, a technician measures 9.8 V across the battery posts. The same meter reads 11.6 V between the engine block and the battery negative post during the same crank. What does this indicate?

  1. Excessive resistance in the earth return path between battery and engine. Correct answer.
  2. The alternator diode trio is shorted.
  3. The starter solenoid contacts are welded closed.
  4. The battery has failed and cannot supply cranking current.

Explanation

A voltmeter placed across a connection or cable during cranking reads the voltage dropped by that resistance. Nearly 2 V lost between the battery negative post and the engine block is far beyond the normal limit of about 0.2 V to 0.5 V, pointing to a corroded or loose earth strap or terminal. The battery posts themselves held 9.8 V, so the battery is not the main culprit.

Question 49Batteries, Charging and Starting Systems

A customer reports that the charge warning lamp glows faintly at idle and brightens as engine speed increases, and charging voltage falls as rpm rises. Which fault best fits these symptoms?

  1. A shorted or grounded rotor field winding. Correct answer.
  2. A slipping alternator drive belt.
  3. A blown main charge fuse.
  4. A worn starter brush set.

Explanation

A field circuit fault such as a grounded rotor winding causes the alternator to lose control of excitation, so output falls as speed rises and the warning lamp receives current through the fault path. A slipping belt would instead show noise, glazing and poor output that often improves briefly with speed, not a progressive decline.

Question 50Batteries, Charging and Starting Systems

An alternator rated at 70 A is fitted to a vehicle whose continuous electrical load with lights, blower and demister totals about 75 A. What is the most likely long-term result?

  1. The battery stays fully charged because the regulator increases voltage to compensate.
  2. The load will be shared equally so neither battery nor alternator is affected.
  3. The alternator will produce more than 70 A once warm and cover the load.
  4. The battery gradually discharges while driving and the alternator runs at or beyond its limit. Correct answer.

Explanation

An alternator must supply the continuous load plus whatever current is needed to recharge the battery. If the load exceeds the rated output, the battery has to make up the deficit and slowly discharges, while the alternator runs at maximum and may overheat. The correct fix is to reduce the load or fit a higher-output unit.