Cert III Auto Electrical key terms

The fixed relationship between voltage, current and resistance in a circuit, expressed as voltage equals current multiplied by resistance. Knowing any two values lets you calculate the third.

The loss of voltage that occurs as current flows through resistance in a conductor or component. Excessive drop in a supply or earth path causes dim lights, slow motors and unreliable electronics.

A circuit where current has only one path, flowing through each component in turn. Current is the same everywhere, while the supply voltage divides across the loads.

A circuit where components are connected across the same two points, so each receives full supply voltage. Total current equals the sum of the branch currents, which is how most vehicle loads are wired.

The practice of using the vehicle body or chassis as the return conductor back to the battery negative terminal. Poor chassis connections here are a common cause of electrical faults.

A wiring arrangement where a dedicated cable carries current back to the battery negative instead of the chassis. Used where low resistance return paths are critical, such as high-current or sensitive circuits.

An electromagnetically operated switch that lets a small control current switch a much larger load current. It protects delicate switches and control modules from high current and voltage spikes.

A diode fitted across a relay or solenoid coil to give the collapsing magnetic field a safe path when power is removed. It prevents damaging voltage spikes reaching control modules and switches.

A deliberately weak link in a circuit that melts and opens the circuit when current exceeds its rating. It protects wiring from overheating and fire, and must be replaced with the correct rating.

A heavy-duty fuse, often a short section of special wire or a bolt-in cartridge, protecting main supply cables. It sits close to the power source to isolate major circuits from short circuits.

The maximum current a conductor can carry continuously without overheating its insulation. It depends on conductor cross-sectional area, insulation type, bundling and ambient temperature.

A test instrument that measures voltage, resistance and current, and often continuity and diodes. Correct range and connection selection are essential to avoid damage or misleading readings.

An accessory that clips around a conductor and measures current from its magnetic field without breaking the circuit. Ideal for checking starter, alternator and parasitic draw currents.

A diagnostic instrument that displays voltage against time, showing the shape and timing of signals. It is used to analyse sensors, injectors, ignition and communication bus waveforms.

Current that continues to flow from the battery after all loads are switched off and modules have gone to sleep. Excessive draw flattens the battery overnight and is traced with a current clamp.

The lead-acid storage device that supplies power for cranking and stabilises system voltage while the engine runs. Its condition is assessed by state of charge, load testing and terminal inspection.

An engine-driven generator that produces alternating current, rectifies it to direct current and charges the battery. It also supplies all running loads once the engine is started.

The control device, usually built into the alternator or managed by the engine computer, that holds charging voltage within a set range. It prevents overcharging and undercharging of the battery.

The high-current path from battery positive through cables, relay or solenoid to the starter motor and back to earth. Poor connections here cause slow cranking and hot cables.

A semiconductor device that allows current to flow in one direction only. It is used for rectification, circuit protection and blocking reverse current flow.

A semiconductor lamp that glows when forward current passes through it. It is long-lived and low current, but requires correct polarity and a suitable series resistance or driver.

An electronic control unit that manages body electrical functions such as lighting, locking, wipers and power windows. It often coordinates sleep states and communicates with other modules over a data bus.

A twisted-pair serial communication network that lets electronic control units exchange data reliably in a vehicle. Faults such as shorts or open wires can disable multiple systems at once.

A resistor fitted at each end of a communication bus to match impedance and prevent signal reflections. Its presence can be checked by measuring resistance across the bus with power off.

The formal name for the CAN protocol, a robust message-based standard used for vehicle networking. Messages carry identifiers and data rather than addressing a single receiver.

A sensor that reports engine speed and crank angle to the engine control module so it can time injection and ignition. Its signal is often a magnetic or Hall-effect waveform.

A sensor that detects magnetic field changes and outputs a switching or analogue voltage signal. Used for position, speed and current sensing without mechanical contact.

The computer that calculates fuel delivery, ignition timing and emission control from sensor inputs. It stores diagnostic trouble codes and controls outputs such as injectors and relays.

A stored code set by a control module when it detects a fault in a monitored circuit or system. The code guides testing but does not by itself identify the failed component.

A device that communicates with vehicle control modules to read codes, live data and perform tests. It complements, but never replaces, physical circuit testing with meters and scopes.

Joining conductors by melting a filler alloy so it wets and bonds the metals. A sound joint is shiny and smooth, and is protected with heat-shrink for mechanical support and sealing.

Forming a permanent electrical and mechanical connection by compressing a terminal onto a conductor with the correct tool. A good crimp is gas-tight and passes a pull test.

A polymer sleeve that shrinks when heated to insulate, seal and strain-relieve a joint or terminal. Choosing the right size and adhesive-lined type improves reliability in wet areas.

The metal contact that joins a conductor to a component, connector or battery post. Correct type, size and crimp quality determine resistance and long-term reliability.

A bundled assembly of conductors, connectors and protective sleeving routed through the vehicle. It is secured and supported to prevent chafing, strain and water entry.

Adhesive cloth or plastic tape used to bind and protect harness conductors. Correct wrapping technique preserves flexibility and resists abrasion and moisture.

Wear of insulation caused by movement or rubbing against a hard surface. It exposes conductors, causing shorts or intermittent faults, and is prevented by clips, conduit and correct routing.

An unintended low-resistance path between a supply conductor and earth or another circuit. It causes excessive current, blown fuses and possible fire or component damage.

A connection with poor metal-to-metal contact, often from corrosion or a loose terminal. It causes voltage drop, heat, dim lights and erratic operation of loads.

A second battery, often deep-cycle, charged from the vehicle and used to run accessories without flattening the starting battery. It needs isolation, correct cable sizing and protection.

The legal and practical duty to identify hazards, assess risk and control them before and during work. In auto electrical work it covers electrical, chemical, thermal and manual handling risks.

Items worn to reduce exposure to hazards, such as safety glasses, gloves, hearing protection and insulated footwear. It is the last line of defence after higher-order controls.

A structured process of identifying hazards, judging likelihood and consequence, and choosing controls. It is documented and reviewed as the task or conditions change.

The procedure of disconnecting a power source, proving it dead and preventing reconnection before work. It protects the technician from shock, burns and unexpected movement.

The obligation to handle and dispose of waste such as batteries, oils, refrigerants and solvents lawfully. It includes spill containment, correct storage and using approved recyclers.