Radio Frequency Interference (RFI): Radio and television interference caused by electromagnetic energy.

RAM (Random Access Memory): Stores temporary information that can be read from or written to by the CPU. RAM can be designed as volatile or nonvolatile.

Recombination Battery: A type of battery that is sometimes called a dry-cell battery because it does not use a liquid electrolyte solution.

Rectification: The process of converting AC to DC current.

Regenerative Braking: Braking energy created by a generator producing electricity. The braking energy is turned back into electricity instead of heat.

Relay: A device that uses low current to control a high-current circuit. Low current is used to energize the electromagnetic coil, while high current is able to pass over the relay contacts.

Reluctance: A term used to indicate a material's resistance to the passage of flux lines.

Reserve Capacity Rating: An indicator, in minutes, of how long the vehicle can be driven, with the headlights on, if the charging system should fail. The reserve capacity rating is determined by the length of time, in minutes, that a fully charged battery can be discharged at 25 amperes before battery cell voltage drops below 1.75 volts per cell.

Resistance: The opposition to current flow.

Resistance Wire: A special type of wire that has some resistance built into it. These typically are rated by ohms per foot. Spark plug wires are an example of resistance wire.

Resistor Block: Consists of two or three helically wound wire resistors connected in series.

Resistive Multiplex Switch: Provides multiple inputs over a single circuit. Since each switch position has a different resistance value, the voltage drop is different. This means a switch can have one power supply wire and one ground wire instead of a separate wire for each switch position.

Reverse Bias: A positive voltage is applied to the N-type material and negative voltage is applied to the P-type material of a semiconductor.

Rheostat: A two-terminal variable resistor used to regulate the strength of an electrical current.

Right-hand rule: Identifies the direction of the lines of force of an electromagnet.

ROM (Read Only Memory): Memory chip that stores permanent information. This information is used to instruct the computer on what to do in response to input data. The CPU reads the information contained in ROM, but it cannot write to it or change it.

Rotor: The component of the AC generator that is rotated by the drive belt and creates the rotating magnetic field of the AC generator.

Saturation: 1. The point at which the magnetic strength eventually levels off, and where an additional increase of the magnetizing force current no longer increases the magnetic field strength.  2. The point where forward-bias voltage to the base leg of a transistor is at a maximum. With bias voltage at the high limits, output current is also at its maximum.

Schematic: An electrical diagram that shows how circuits are constructed, but not details such as color codes.

Secondary Circuit: All the components that carry voltage to the combustion chamber of the internal combustion engine.

Secondary Coil Windings: One of the two wire coils in the ignition coil. This winding has several thousand turns and is where low voltage will be transformed to high voltage.

Self-induction: The generation of an electromotive force by a changing current in the same circuit.

Semiconductor: An element that is neither a conductor nor an insulator. Semiconductors are materials that conduct electric current under certain conditions, yet will not conduct under other conditions.

Sending Unit: The sensor for a gauge. It is a variable resistor that changes resistance values with changing monitored conditions.

Sensor: Any device that provides an input to the computer.

Separators: Normally constructed of glass with a resin coating. These battery plates offer low resistance to electrical flow but high resistance to chemical contamination.

Sequential Logic Circuits: Flip-flop circuits in which the output is determined by the sequence of inputs. A given input affects the output produced by the next input.

Sequential Sampling: The process that the MUX and DEMUX operate on. This means the computer will deal with all of the sensors and actuators one at a time.

Series Circuit: A circuit that provides a single path for current flow from the electrical source through all the circuit's components and back to the source.

Series-parallel Circuit: A circuit that has some loads in series and some in parallel.

Servomotor: An electric motor that produces rotation of less than a full turn. A feedback mechanism is used to position itself to the exact degree of rotation required.

Shell: The electron orbit around the nucleus of an atom.

Short: An unwanted electrical path; sometimes this path goes directly to ground.

Shorted Circuit: A circuit that allows current to bypass part of the normal path.

Shunt: More that one path for current to flow.

Shunt Circuits: The branches of the parallel circuit.

Shutter Wheel: A metal wheel consisting of a series of alternating windows and vanes. It creates a magnetic shunt that changes the strength of the magnetic field from the permanent magnet of the Hall-effect switch or magnetic pulse generator.

Sine Wave: A waveform, as viewed on an oscilloscope, that shows voltage changing polarity.

Single Phase Voltage: The sine wave voltage induced in one conductor of the stator during one revolution of the rotor.

Slave Module: Controller on the network that must communicate through a master controller.

Slip Rings: Rings that function much like the armature commutator in the starter motor; however, they are smooth rather than segmented.

Smart Sensors: Sensors that are capable of sending digital messages on the data bus.

Solenoid: An electromagnetic device that uses movement of a plunger to exert a pulling or holding force.

Specific Gravity: The weight of a given volume of a liquid divided by the weight of an equal volume of water.

State of Charge: The condition of a battery's electrolyte and plate materials at any given time.

Static Electricity: Electricity that is not in motion.

Stator: The stationary coil of the AC generator where current is produced.

Stepped Resistor: A resistor that has two or more fixed resistor values.

Stepper Motor: An electric motor that contains a permanent magnet armature with two or four field coils. Can be used to move the controlled device to whatever location is desired. By applying voltage pulses to selected coils of the motor, the armature will turn a specific number of degrees. When the same voltage pulses are applied to the opposite coils, the armature will rotate the same number of degrees in the opposite direction.

Stranded Wire: A conductor comprised of many small solid wires twisted together. This type of conductor is used to allow the wire to flex without breaking.

Sulfation: A condition in a battery that reduces its output. The sulfate in the battery that is not converted tends to harden on the plates, resulting in permanent damage to the battery.

Supplemental Bus Networks: Bus networks that are on the vehicle in addition to the main bus network.

Termination Resistors: Used to control induced voltages. Since voltage is dropped over resistors, the induced voltage is terminated.

Thermistor: A solid-state variable resistor made from a semiconductor material that changes resistance in relation to temperature changes.

Timer circuit: 1. Uses a bimetallic strip that opens as a result of the heat being generated by the current flow.  2. An electronic circuit usually made up of capacitors resistors and transistors used for a time delay for turning a circuit on or off.

Timing Disc: Known as an armature, reluctor, trigger wheel, pulse wheel, or timing core. It is used to conduct magnetic lines of force.

Tracer: A thin or dashed line running the length of a wire that is a different color than the base color of the insulation.

Trailing Edge: In a Hall-Effect switch, the edges of the rotating blade that exit the switch.

Transducer: A device that changes energy from one form to another.

Transistor: A three-layer semiconductor used as a very fast switching device.

Turn-on Voltage: The voltage required to jump the PN junction and allow current flow.

Valence Ring: The outermost orbit of the atom.

Variable Resistor: A resistor that provides for an infinite number of resistance values within a range.

Volt: The unit of measurement for the amount of electrical force.

Voltage:  It is the electrical pressure that causes electrons to move through the circuit. One volt is the amount of pressure (Electromotive Force) required to move one amp of current through one ohm of resistance.

Voltage Drop: A resistance in the circuit that reduces the electrical pressure available after the resistance. The resistance can be either the load component, the conductors, any connections, or unwanted resistance.

Voltage Regulator: Used to control the output voltage of the AC generator, based on charging system demands, by controlling field current.

Voltmeter: A test meter used to measure voltage in a circuit. 

Wake-up Signal: An input signal used to notify the body computer that an engine start and operation of accessories is going to be initiated soon. This signal is used to prepare the circuits that will be processing information.

Watt: The unit of measure of electrical power, which is the equivalent of horsepower. One horsepower is equal to 746 watts.

Weather-pack Connector: A type of connector that seals the terminal ends. This type connector is used in electronic circuits.

Wireless Networks: Connection of modules together to transmit information without the use of physical connection by wires.

Wiring Diagram: An electrical schematic that shows a representation of actual electrical or electronic components and the wiring of the vehicle's electrical system.

Wiring Harness: A group of wires enclosed in a conduit and routed to specific areas of the vehicle.

Zener Diode: A diode that allows reverse current to flow above a set voltage limit. Used as a voltage regulator.

Zener Voltage: The voltage that is reached when a diode conducts in reverse direction.