ASE S6 Electrical/Electronic Systems (School Bus) key terms

A measurement of the difference in voltage between two points in a live circuit, used to find resistance caused by corroded, loose, or undersized connections without disconnecting the load.

Current that continues to flow from the battery after all switches are off, caused by modules, relays, or accessories that stay powered; measured in milliamps to find a battery drain.

The return path for electrical current through the metal frame and body of the bus; a poor ground connection causes dim lights, slow cranking, and erratic module behavior.

A drawing that shows the electrical components of a circuit and how they are connected, using standardized symbols, wire colors, and pin numbers to trace faults.

The metal pin or socket inside a wiring connector that carries current; terminals can be spread, pushed back, or corroded, creating high resistance or an open circuit.

A handheld test instrument that measures voltage, resistance, current, and often frequency or duty cycle; the primary tool for diagnosing electrical faults on a school bus.

A two-wire serial data bus that lets electronic modules share information; bus faults such as shorted or open CAN lines can disable lighting, gauges, and warning systems.

An electronic module that controls body electrical functions such as lights, wipers, door locks, and warning devices, often receiving inputs over a data bus instead of direct wiring.

A vehicle electrical architecture in which switches and modules communicate over shared data networks rather than individual dedicated wires, reducing harness size and adding diagnostic complexity.

A test that applies a heavy current load to a battery and measures how well it holds voltage, revealing a battery that is charged but cannot deliver cranking power.

The current a battery can deliver for 30 seconds at 0 degrees Fahrenheit while staying at or above 7.2 volts; the rating used to match a battery to the bus engine.

The number of minutes a fully charged battery can supply 25 amps at 80 degrees Fahrenheit before falling below 10.5 volts, indicating how long it can run loads if the alternator fails.

The percentage of a battery's full capacity that remains, commonly estimated from open-circuit voltage after the battery has rested and surface charge has been removed.

The density of battery electrolyte compared with water, measured with a hydrometer to estimate state of charge in flooded lead-acid batteries; not applicable to sealed AGM batteries.

A heavy-duty manual switch, often required on school buses, that disconnects the battery from the vehicle electrical system for service or emergency shutdown.

The current a battery can deliver at 32 degrees Fahrenheit for 30 seconds at or above 7.2 volts; a warmer-temperature rating that is higher than the CCA rating.

An electromagnetic switch mounted on or near the starter that connects battery power to the starter motor and often engages the drive pinion when the ignition is turned to start.

A remote electromagnetic switch that uses a low-current control circuit to operate the high-current starter solenoid circuit, protecting the ignition switch from heavy current.

A switch that prevents the starter from cranking unless the transmission is in neutral or park, or the clutch is depressed; a common cause of a no-crank condition.

A test performed while cranking to measure excessive resistance in battery cables, ground straps, and solenoid contacts; more than about 0.5 volts on a cable indicates a problem.

A circuit that blocks starter operation under unsafe conditions, such as an open emergency exit, an engaged stop arm, or a hood that is open for service.

The alternator, regulator, battery, and wiring that supply electrical power and recharge the battery while the engine runs; failure causes warning lamps and eventual battery drain.

A belt-driven generator that produces alternating current and rectifies it to direct current to power the bus electrical loads and recharge the battery.

A device, often built into the alternator or controlled by the engine computer, that limits alternator field current to hold charging voltage within a specified range.

A dashboard warning light that illuminates when charging voltage is below or above the normal range, alerting the driver to an alternator or belt fault.

A clamp-on current probe used with a multimeter to measure charging or load current without disconnecting cables, useful for checking alternator output on high-current school bus circuits.

The adjustment of headlight direction so the beam pattern meets inspection requirements; improper aim reduces visibility and can fail a school bus safety inspection.

A headlight assembly in which the lens, reflector, and filament are one sealed unit; when the filament fails the whole unit is replaced.

Light-emitting diode lamps that draw low current and last long, commonly used for school bus warning and marker lights; polarity matters and some circuits may not work with standard bulb testers.

A module or relay that interrupts current to the turn signal and hazard lamps to produce the flashing pattern; a failed flasher causes no flash or a fast-flash condition.

A circuit that flashes all four turn signal lamps simultaneously, used when a bus is stopped or disabled, and required to function independently of the ignition switch.

The instrument panel assembly containing speedometer, tachometer, fuel, temperature, oil pressure, and warning indicators; often driven by data bus messages rather than direct sensors.

Programmed setting that matches the speedometer and odometer to the tire size and axle ratio of the bus; incorrect calibration affects recorded mileage and speed readings.

A sound-producing device that alerts the driver to conditions such as low oil pressure, high temperature, or an open emergency exit, often paired with a dash indicator.

A warning system that sounds when an emergency exit door, window, or roof hatch is opened, alerting the driver and often triggering a dash indicator.

The swing-out stop sign on the left side of a school bus, deployed with flashing red lights when loading or unloading students; its circuit includes a switch, motor, and warning interlocks.

A pivoting arm at the front of the bus that swings out to guide students away from the bus during loading and unloading; driven by an electric motor or actuator with position switches.

The school bus warning light system with red and amber lamps on the front and rear; amber warns of an approaching stop and red signals that students are loading or unloading.

A system that requires the driver to walk to the rear of the bus and press a button after each route, confirming no child remains aboard; failure triggers an alarm.

A communication radio used by the driver to contact dispatch; installation includes antenna, power, and ground connections that must be secure to avoid noise and interference.

A device that reports the bus location and often telemetry over a wireless network; it requires a stable power feed, ground, and antenna connection to function reliably.

Interior and exterior video cameras on a school bus that record student and traffic activity; power, ground, and video cable faults cause missing or distorted images.