NABTEB Automobile Electrical Works key terms

The relationship stating that voltage equals current multiplied by resistance (V = I × R). It lets a technician calculate any one of the three quantities when the other two are known in a circuit.

A circuit in which components are connected end to end so that the same current flows through each one. Total resistance is the sum of the individual resistances, and a break stops all current.

A circuit in which components are connected across the same two points, so each receives the full supply voltage. Total resistance is always lower than the smallest individual resistance in the network.

The opposition a material offers to the flow of electric current, measured in ohms. In vehicles it arises from conductors, loads, connections and corroded joints, and it converts electrical energy into heat.

The reduction in voltage across a component, conductor or connection as current flows through it. Excessive drop along a cable or earth point indicates high resistance and causes dim lights or slow cranking.

The production of a voltage in a conductor when it moves through a magnetic field or when the field around it changes. It is the principle behind alternators, ignition coils and many sensors.

A rechargeable battery in which lead plates and lead oxide plates sit in diluted sulphuric acid. Each cell produces about 2.1 volts, so a six-cell battery gives roughly 12.6 volts at rest.

A rating showing how much current a battery can deliver for 30 seconds at minus 18 degrees Celsius while staying above 7.2 volts. It indicates the battery's ability to start an engine in cold weather.

The density of a liquid compared with water, used with a hydrometer to check battery electrolyte strength. A fully charged cell reads near 1.260 to 1.280; a low reading suggests discharge.

A belt-driven generator that produces alternating current which is rectified to direct current for charging the battery and running vehicle loads. Its output is regulated to about 13.8 to 14.5 volts.

A control device that limits alternator field current so charging voltage stays within a safe range. It prevents overcharging the battery and protects bulbs and electronic modules from excessive voltage.

A set of diodes inside an alternator that converts alternating current into direct current. A failed diode causes poor charging output and may produce a noticeable ripple in the charging voltage.

A heavy-duty direct current motor that turns the engine flywheel through a pinion so combustion can begin. It draws very high current, often several hundred amperes, from the battery.

An electromagnetic switch that both engages the starter drive pinion with the flywheel and closes the heavy contacts feeding current to the starter motor. It is operated by the ignition switch circuit.

A transformer that steps battery voltage up to thousands of volts to jump the spark plug gap. It has a low-resistance primary winding and a high-resistance secondary winding around an iron core.

A device screwed into the combustion chamber that carries high voltage across an air gap to ignite the fuel mixture. Electrode gap and heat range must match the engine manufacturer's specification.

The moment, measured in degrees of crankshaft rotation, at which the spark occurs relative to top dead centre. Correct timing gives full power; wrong timing causes knocking, hard starting or overheating.

A mechanical unit that routes the high-voltage coil output to each spark plug in firing order and often triggers the spark. Many modern engines replace it with coil-on-plug or wasted-spark systems.

The correct vertical and horizontal setting of a headlamp beam on the road. Poor aim dazzles oncoming drivers or reduces the driver's view, and is checked with a beam setter during inspection.

The low headlamp setting used in traffic, angled downwards and towards the kerb so the road ahead is lit without blinding other road users. Its pattern is set by the lamp reflector and lens.

A circuit that makes all four direction indicators flash together to warn other road users of a stopped or slow vehicle. It usually works through a separate switch and often its own flasher unit.

A thermal or electronic device that interrupts current to the indicator bulbs so they flash at a steady rate. A fast flash rate often signals a failed indicator bulb.

The practice of using the metal body and chassis as the return path for current back to the battery negative terminal. Poor earth connections cause many intermittent electrical faults.

A bundled set of insulated wires with connectors and terminals, routed through the vehicle to link electrical components. Colour codes, loom tape and clips keep it organised and protected from chafing.

A deliberately weak link that melts and opens the circuit when current exceeds its rating, protecting wiring and components. It must always be replaced with one of the same current rating.

An electromagnetic or electronic switch that lets a small control current operate a circuit carrying much larger current. It reduces load on switches and shortens heavy cables to the battery.

A resettable protective device that opens a circuit on overload and can be reset manually or automatically. It is used where a blown fuse would be inconvenient to replace, such as window lift circuits.

A test instrument combining voltmeter, ammeter and ohmmeter functions, often with continuity and diode tests. It is the basic tool for checking supply, earth, resistance and current in vehicle circuits.

A check made with an ohmmeter or buzzer to confirm that a conductor path is unbroken and has very low resistance. The circuit must be isolated and unpowered before testing.

A break in a circuit that stops current flowing, such as a broken wire, loose terminal or blown fuse. It shows as infinite resistance and the affected component will not operate.

An unintended low-resistance path that lets current bypass the load, often between a live wire and earth. It causes excessive current, blown fuses or fire risk if protection fails.

A tool for drawing electrolyte from a battery cell and measuring its specific gravity with a float. Readings from all cells are compared to judge state of charge and detect a faulty cell.

A wrench set to tighten fasteners to a specified turning force, usually in newton metres. It is used on battery terminals, cylinder head bolts and other joints where overtightening causes damage.

A hand tool whose working end is covered with approved insulating material to protect the user from electric shock. It is required when working near live high-voltage systems such as electric vehicle batteries.

The precautions taken when working on electric and hybrid vehicle systems rated above 60 volts, including isolation, lockout tagging, insulated gloves and proving the circuit is dead before touching it.

A drawing that shows electrical components and the wires connecting them, with colour codes, terminal numbers and symbols rather than physical positions. It is the main aid for tracing faults.

The standard system of labelling component and connector pins, such as 30 for permanent live and 15 for ignition live, so diagrams and wiring can be matched reliably during diagnosis.

An optical device placed in front of a headlamp to check the height and direction of the beam pattern against the manufacturer's specification. It is used after lamp or suspension work.