SVP Auto Electrician key terms

Clothing and equipment worn to reduce the risk of injury at work, such as safety glasses, insulated gloves, hearing protection and steel-toe boots. It supports, but never replaces, safe procedures and correct tool use.

A structured check of a job before starting it, identifying hazards, judging how likely and how severe harm could be, and recording the controls needed to make the task acceptably safe.

A procedure for isolating an energy source, such as a battery or high-voltage system, then locking the isolator and attaching a warning tag so the circuit cannot be re-energised while someone works on it.

A handheld instrument that measures voltage, resistance and often current and continuity, showing results on a digital display. Selecting the correct function and range before connecting the probes prevents damage to the meter and the circuit.

A test instrument that draws a signal as a graph of voltage against time. It reveals shape, amplitude, frequency and brief glitches that a multimeter averages away, making it useful for sensors, injectors and network signals.

An accessory that snaps around a conductor and measures the current flowing in it from the surrounding magnetic field, without breaking the circuit. Clamp-on types suit high currents such as starter or alternator output.

An instrument that applies a high test voltage to a circuit and measures leakage, showing whether cable and winding insulation is sound. It is used on motors, heaters and wiring, never on electronic modules.

A wrench that clicks or otherwise signals when a set tightening torque is reached, so fasteners such as battery terminals and mounting bolts are tightened to the maker's figure without damage or loosening in service.

The relationship stating that voltage equals current multiplied by resistance (V = I × R). It lets a technician predict how a circuit will behave and calculate the missing value when two of the three quantities are known.

A circuit in which components are connected end to end so the same current flows through each one. Total resistance is the sum of the parts, and the supply voltage is shared between the components.

A circuit in which components are connected across the same two points, so each receives the full supply voltage. Current divides between the branches and total resistance is lower than the smallest branch resistance.

The difference in voltage measured across a component, or along a cable, while current is flowing. Excessive drop in cables or connections shows unwanted resistance and is found by testing under load.

The process by which a changing magnetic field produces a voltage in a conductor. It is the principle behind alternators, ignition coils and many speed and position sensors.

A semiconductor device that lets current flow in one direction only. In vehicles it rectifies alternator output, suppresses voltage spikes from coils and isolates circuits so current cannot back-feed.

An electrically operated switch in which a small coil current moves contacts to control a much larger load current. It lets thin control wiring and a small switch operate high-current devices such as lamps or motors.

The current value at which a fuse is designed to melt and open the circuit. Fitting a fuse of higher rating than specified removes the protection and can cause overheating, melted wiring or fire.

A short length of special wire, usually in a battery feed, that melts and breaks the circuit when current rises far above normal. It protects main circuits that a normal blade fuse cannot handle.

A connection between a circuit and the metal body or frame, which acts as the return path to battery negative. Poor ground connections cause dim lamps, slow motors and false sensor readings.

A drawing showing the components of an electrical system and how they are connected, using standard symbols, wire colours and pin numbers. It is the main reference for tracing circuits and planning tests.

The amount of conducting metal in a cable, usually stated in square millimetres, which sets how much current it can carry safely. Undersized wire overheats; oversized wire wastes cost and weight.

The current a battery can deliver for 30 seconds at minus 18 °C while its voltage stays above a stated level. It indicates how well the battery will crank an engine in cold conditions.

How full a battery is, expressed as a percentage of its capacity and estimated from open-circuit voltage or a conductance test after the battery has rested. It is not the same as battery health.

A belt-driven generator that produces alternating current, rectifies it to direct current and supplies the vehicle's loads while recharging the battery. Its output is controlled by a built-in regulator.

A heavy-duty switch, often mounted on the starter, that closes the high-current circuit from battery to starter motor when the ignition is operated. It may also engage the drive pinion.

The three main types of vehicle lamp bulb or module: halogen uses a heated filament, HID uses a high-voltage arc, and LED uses semiconductors. Each needs different testing methods and safety precautions.

A device or electronic function that switches the indicators on and off at a regular rate, and produces the faster flash or no flash that warns the driver of a failed bulb.

A switch on the brake pedal that closes when the pedal is pressed, lighting the stop lamps and often signalling the cruise control or transmission control module. Its adjustment affects when the lamps come on.

An electronic unit that operates and monitors body functions such as lamps, wipers, locks and windows, often receiving requests over a network from other modules and from switches.

A contact inside the wiper motor gearbox that keeps the motor powered after the driver switches off, so the blades return to their rest position at the bottom of the screen.

A safety feature in a power window system that detects extra motor load or a change in speed when an obstacle is met and reverses the window to prevent injury.

A computer with inputs, outputs and memory that runs a control strategy for an engine, transmission, brake or body system, and stores fault codes when signals fall outside expected limits.

A sensor that produces a voltage when a magnetic field passes through its semiconductor element. Used for crank and cam position, wheel speed and current measurement, it gives a fast switching signal.

A device that converts an electrical command from a control unit into mechanical action, such as a solenoid, motor, relay or injector. Testing checks its supply, its control signal and the mechanical result.

Controller area network: a two-wire differential serial network that lets control units exchange data at high speed. A shorted or open wire can disrupt communication across many systems at once.

Local interconnect network: a single-wire, low-speed serial network used for simple body devices such as door modules, mirrors and sensors, which act as slaves to one master control unit.

A numbered code stored by a control unit when it detects a fault or an implausible signal. The code identifies the circuit or system involved, but not necessarily the exact cause.

A diagnostic device that connects to the vehicle's diagnostic socket to read fault codes, live data and stored conditions, and to command actuators for testing. Capabilities vary with software and vehicle coverage.

The current values of sensor inputs and calculated outputs that a control unit reports to a scan tool while the vehicle runs, used to compare actual behaviour with expected values.

A measurement of the small current a vehicle takes from the battery after all modules have gone to sleep, used to find a component that is draining the battery overnight.