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Technical Terms P-Z

Parallel Circuit -

A circuit in which current can flow independently through several components at the same time. See Series Circuit.

Polarity -

Polarity is the designation which indicates the direction of flow of a current from a source upon completion of a circuit. The positive is the point at the source from which the current flows- the negative is the point at the source at which current returns.

Polarity-Protested Connector -

A multiple-cavity connector that can be connected in only one way, either to a mating connector or to a component.

Printed Circuit -

An electrical conductor consisting of thin metal foil paths adhered to a flexible plastic backing also called a PC board. PCs are used primarily in OEM instrument clusters and other electronic devices.

Relay -

An electromechanical device consisting of an electromagnetic coil, a fixed core and a movable armature. The armature is generally connected to an electrical switch that moves according to whether the coil is energized. Like a switch, a relay is used to open and close circuits, but is usually activated by another switch in a remote location.

Resistance -

In electricity, the restriction to electron flow present in an electrical circuit, expressed in ohms.  The higher the resistance, the more current must flow to overcome it. The more current flow through an area of high resistance, the hotter the wire will become.

Resistor -

Any conductor that permits electron movement but retards it. Examples include tungsten and nickel.

Rheostat -

A variable resistor, operated by knob or handle, used to vary the resistance in a circuit. It consists of a coil of resistance wire and a movable contact or wiper that creates more or less resistance in the circuit, depending on how many coil windings it allows the current to pass through. When used as a switch, it allows a continuous setting. An example is the dimmer control for instrument-panel illumination.

Ring Terminal -

A connector used to attach a wire to a screw or stud terminal. The ring is sized to the mating screw. Ring terminals are the least likely to vibrate loose in rugged applications such as racing. Comes in soldered and solderless versions.

Schematic -

Another word for a wiring diagram. A drawing system for portraying the components and wires in a car’s electrical system using standardized symbols

Sending Unit -

Used to operate a gauge. Contains a variable resistance that modifies current flow according to the condition or system being monitored. The variations in current flow are then interpreted by the gauge.

Series Circuit -

A circuit in which current has to pass through a series of components, one at a time.

Series/Parallel Circuit -

A circuit where some components are wired in series, others in parallel. An example is two loads wired in parallel with each other, but in series with the switch that controls them.

Short Circuit -

An undesirable condition in which current is permitted to bypass the load, returning to the source without doing any useful work. “Shorts” are usually a result of a bare conductor wire accidentally touching a grounded metal part between the load and source.

Shrink Wrap -

An insulating material used to protect wire splices and junctions at terminals. Upon application of open flame or heat, the wrap shrinks to fit tightly on the wire or terminal.

Simple Circuit -

The simplest circuit included an electrical source, a load and some wire to join them.

Single-Wire Circuit -

Generally used in production automobiles, in which one wire brings current to the load and the car’s frame acts as the return path (ground).

Solderless Connector -

Any connector or terminal that can be installed to a wire without the use of solder. They usually are crimped in place using a special crimping tool. Examples are ring terminals, spade terminals, disconnect terminals, butt connectors, closed-end connectors and snap-splice connectors. Ring and spade terminals also come in solder versions.

Solenoid -

An electron mechanical device consisting of an electromagnetic coil surrounding a movable metal core, or plunger. The movable core is connected to various mechanisms to accomplish work.

Spade Terminal -

A terminal used to connect a wire to a screw or stud terminal. It has two forked ends, wither straight or with upturned tips. They’re more convenient to install than ring terminals, but slightly less secure for rugged duty. Comes in soldered and solderless versions.

Split Loom -

Flexible, corrugated conduit used to bundle wires into harnesses.

Terminal Block -

A plastic or resin assembly containing two rows of terminal screws. Used to join the circuit in several wiring harnesses. Occasionally contain, or are part of, a fuse panel.

Test Lamp, 12-Volt -

A test instrument consisting of an indicator lamp wired into the handle of a metal probe. When the probe contacts a live circuit, current flows through the lamp, lighting it, and to ground through an attached wire and alligator clip. Used to test for voltage in live circuits only. Also called a continuity tester.

Test Lamp, self-powered -

A test device containing an indicator lamp and a built-in battery. Used to test continuity of circuits not containing voltage at the time of the test (dead circuits). This is the type used to test continuity in a harness before it is installed in the car.

Thermistor -

The electrical element in a temperature-sending unit that varies its resistance in proportion to temperature. Unlike most electrical conductors, in which resistance increases as temperature rises, resistance in a thermistor decreases. Thermistors are made from the oxides of cobalt, copper, iron or nickel.

Tracer -

A stripe of a second color applied to a wire insulator to distinguish that wire from another one with the same color insulator. Can be simulated by running a waterproof magic marker along a wire.

Volt -

A measure of electrical force, or pressure.

Voltage -

Voltage is the force (or pressure) of electricity in the wire. One volt is defined as the electrical pressure which when steadily applied to a conductor having a resistance of one ohm will produce a current of one ampere.  Older cars run on six volt systems and newer (most 1955 and later) utilize twelve volt systems.

Voltage Drop -

Any condition in a circuit that causes voltage to be reduced. This could be an intentional load or an unintentional drop caused by a faulty or corroded terminal. All wire, no matter how low the resistance, shows at least a trace of voltage drop. The portion of voltage which is consumed in a particular part of a circuit.

Voltage Regulator -

An electromechanical or electronic device that monitors voltage in the vehicle’s electrical system to control generator output within a narrow range. This provides enough current to operate electrical devices while preventing battery overcharge.

Voltmeter -

1. An instrument-panel gauge that measures system voltage. When the engine is not running, the voltmeter indicates battery voltage, which should be 12-13 volts in a 12-volt system. When engine is running, voltmeter indicates total system voltage, or combined voltage output of generator and battery. 2. A test instrument that measures voltage in an electrical circuit. Used to check continuity and determine voltage drop in specific circuits of car’s electrical system.

VOM (volt-ohmmeter) -

A two-in-one test instrument. For convenience, a volt-meter and an ohmmeter are mounted in the same case and share a common readout and test leads.

Warning Lamp -

An instrument-panel display used to inform the driver when something undesirable has happened in the monitored circuit or system, such as an overheated engine or a sudden loss of oil pressure. The driver is required to take action when a warning lamp lights. The action is often to shut down the engine to prevent damage.

Watt -

The unit of electrical power. Watts are equal to volts multiplied by amperes.

Wire -

A slender rod or filament of drawn metal