SECONDARY CIRCUIT- In an ignition circuit, all components are operating on coil (high) voltage.

SECONDARY WIRE- Wire used in a vehicle ignition system. It carries high voltage from the coil to the spark plugs.

SECONDARY WIRE RESISTANCE- A test performed to check condition of a spark plug or coil wire.

SECTOR SHAFT- Output gear in a recirculating ball gearbox.

SEMICONDUCTOR -Substance that acts as an insulator or conductor, depending upon conditions.

SENSOR- Device that monitors and reports a condition to the vehicle computer.

SENSOR ROTOR- A toothed wheel that operates at the same rpm as the vehicle wheel.

SEPARATOR- An insulating material placed between the plates of a battery.

SERVO- Piston that operates a band in an automatic transmission.

SERVO ACTION- Situation in which the primary shoe of a drum brake system helps apply the secondary shoe.

SHAFT RUNOUT- Wear or damage (bending), causing a shaft not to run true around its axis.

SHIFT FORK- Device that physically moves the synchronizer and gear together as a result of shift lever movement.

SHIFT LEVER- The handle operated by the vehicle operator to shift from gear to gear manually.

SHIFT LINKAGE ADJUSTMENT- Making sure the transmission linkage positions match the gear selector positions.

SHIFT RAIL- A manual transmission linkage that is contained within the transmission case.

SHOCK ABSORBER- Device that uses air or hydraulic pressure to dampen up-and-down motion of a vehicle.

SHORT CIRCUIT- Excess current flow that occurs when a conductor touches ground.

SHORTED CONDENSER- One with a direct electrical connection to ground.

SIDEWALL- Portion of a tire between the tread and bead.

SIMPLE CIRCUIT- One consisting of a power source, a load, and conductors.

SLOW CHARGER- One that feeds a small current into the battery over a long period of time.

SOLENOID ACTUATOR- One with a moving metal core that is actuated by an induced magnetic field.

SPARK PLUG- Devices that emit an electrical arc at the tip to ignite the air-fuel mixture in an engine cylinder.

SPARK TEST- Check of the spark intensity (brightness and length of arc).

SPECIFIC GRAVITY- Weight or density of a liquid.

SPIDER GEARS- Idler and axle gears in the differential that drive the rear axles of a vehicle.

SPINDLE- Stationary shaft used to support rotating wheel assembly on nondriving wheels.

SPONGY BRAKES- Braking system that is "soft" feeling, usually as a result of air trapped in the hydraulic system.

SPRING RATE- The stiffness or tension; amount of weight required to compress or bend a spring.

STARTER CURRENT DRAW TEST- Starting test that establishes the number of amps used by the starting system.

STARTER GROUND CIRCUIT RESISTANCE TEST- Check of all parts between the battery negative and the starting motor.

STARTER MOUNTED SOLENOID- One with a plunger that moves to engage the pinion gear with the flywheel gear.

STARTER RELAY- Device that uses a small current flow from the ignition switch to control a larger current flow to the starter solenoid.

STARTER SOLENOID- A high current relay that energizes the starter motor.

STARTING HEADLIGHT TEST- Starting test conducted with the headlights turned on to provide a load on the battery.

STARTING SYSTEM- Electric motor and other components used to rotate the engine until it starts.

STATIC IMBALANCE- Lack of balance that causes a wheel to vibrate up and down as it rolls.

STATOR- The stationary magnetic field in a generator. Also, component of a torque converter that improves oil circulation and thus, torque.

STATOR TEST- Ohmmeter check for open and shorted windings in the stator.

STEERING AXIS INCLINATION- Angle formed by the inward tilt of the ball joints, kingpin, or struts.

STEERING COLUMN- Assembly consisting of the steering wheel, steering shaft, ignition key mechanism, and associated parts.

STEERING GEARBOX- Gear assembly that turns rotary motion into linear (straight line) left-right motion.

STEERING KNUCKLE- Component that provides support for the wheel spindle or bearings surrounding an axle.

STEERING LINKAGE- Components connecting the steering gearbox to the steering knuckles.

STEERING SHAFT- Component that transfers turning motion from the steering wheel to the steering gearbox.

STEERING SYSTEM- The components that allow the operator to change direction of a vehicle.

STEERING WHEEL PLAY- Excessive movement of the steering wheel without causing any front-wheel movement.

STIFF CLUTCH PEDAL- A condition caused by binding or other restriction in the clutch mechanism, making the pedal hard to depress.

STRUT ASSEMBLY- Suspension component combining shock absorber, coil spring, and upper damper unit. It replaces the upper control arm.

STRUT CARTRIDGE- Replaceable shock absorber unit on a MacPherson strut.

STRUT ROD- Rod that fastens to the control arm and frame to keep the control arm properly oriented.

SUSPENSION SYSTEM- Components that let the wheels move up and down without body movement.

SWAY BAR- A stabilizer that keeps the vehicle body from leaning excessively in turns.

SYNCHRONIZER- Assembly of hub, sleeve, and other components that locks the selected output gear to the output shaft to transmit power. It permits meshing of gears with grinding.