Step by step instructions on how an automotive electrical system works. This
article pertains to all vehicles.
- The electrical system of any vehicle performs
the same function, to deliver and monitor electrical power to various devices and sensors
while under control of a
Step 2 - A wiring harness is used to connect various
devices and sensors to either control, or send feedback data to the computer. The
harness is also used to control the lighting system such as
Step 3 - A wiring harness has many connectors that
serve as an extension which allows routing to devices which are obscurely located.
Step 4 - Connectors are disconnected by depressing
a small tab on the side of the connector. Once apart, the male side of the connector
is designed with terminals that protrude outward, which fit into sockets on the
female side. (Note: Some connectors possess a safety tab which must be removed before
the connector can be disassembled.)
Wiring Harness Connector
Step 5 - A device connector is used to connect
to a particular item such as an ignition coil which is shown here. A safety is used
to securely attach the connector to a device, which adds an extra layer of protection
from accidental disconnection. This safety clip must be removed before the connector
can be released.
Electrical Connector Disassembled
Step 6 - An electronic throttle control actuator
is responsible for metering air flow into the engine which control engine RPM (revolutions
per minute.) Using a throttle control sensor located near the foot pedal supplies
feedback data to the computer. The throttle control system is integrated into the
Electrical Connector with Safety
and traction control systems. In older vehicles throttle action was performed by
a manually controlled throttle cable, which was actuated by the drive's right foot.
Step 7 - The
Electronic Throttle Actuator
controller is an electronic system that helps prevent the wheels from
skidding in panic stop conditions and is integrated into the traction control system.
Step 8 - Sensors provide feedback data to the main
computer which in turn will illuminate a warning light or perform an action such
as shutting the engine down when engine oil pressure has decreased.
Anti-Lock Brake System Controller
Step 9 - Other sensors, such as the camshaft angle
sensors use thin metal windings which break a magnetic field as the shaft rotates
causing a pulse that is sensed by the computer.
Brake Fluid Level Sensor
Step 10 - A power distribution center is used to
route positive battery power throughout the vehicle via relays and fuses. This center
is powered directly off of the positive post of the
Camshaft Angle Sensors
- Inside the PDC are many
which protect and control many electrical circuits such as fuel pump
and fuel injection systems.
Step 12 - A set of control relays act as the main
switching center of electrical power. These relay's act as electronic switches that
are controlled by the computer or by a manual switch. Once engaged, the relay connects
a circuit which actives a particular device.
Fuses and Relays
Step 13 - A set of large amperage fuses protect
high amperage circuits such as the cooling fan, starter solenoid and headlights.
A observation window is provided to inspect the fuse integrity.
Step 14 - Medium duty fuses are used to protect
average vehicle amperage such as power windows and seat heaters. These fuses also
provide an observation window which is needed for inspection.
Large Amperage Fuse
Step 15 - Finally low amperage fuses are used to
protect smaller amperage circuits such as tail lights and interior lighting. These
fuses are easily checked using a
Medium Duty Fuse
Step 16 - The battery supplies both positive and
ground circuits which complete the electron cycle, the positive circuit starts at
the PDC via the battery.
Low Amperage Fuse
Step 17 - The
Positive Battery Input
is powered by the engine via a serpentine belt. This unit creates electrical power
by utilizing an armature and copper windings which are connected using brushes.
While in operation (engine running) this unit supplies power for the vehicle while
charging the battery.
Step 18 - The starter motor is designed to turn
the engine over when the ignition switch is activated. This device pulls the most
amperage of all components encompassed within a vehicle, (hybrid and electric vehicles
Step 19 - The ignition switch is what controls
the electrical system within a locking mechanism that utilizes a key for safety.
This key possess a frequency chip as an added theft deterrent.
Step 20 - An information control center is used
for interior controls such cell phone, GPS and audio system adjustments.
Step 21 - Electronic climate controls enable the
driver and passengers to adjust temperature in a particular section of the vehicle
such as engaging the
Information Control Center
Step 22 - The instrument cluster is used to monitor
engine and others system via gauges and warning lights.
Climate Control Center
Step 23 - There and many switches that are used
to control various items such as door locks and headlights. These switches are user
controlled and can be overridden by the main computer.
Step 24 - Interior lighting controls are automatically
illuminated by the computer, they can also be controlled by the driver.
Door Lock Switch
Step 25 - The lighting system is used to illuminate
the vehicle for safety and convenience. The rear lights include, tail, brake, reverse
and license plate bulbs.
Step 26 - The front of a vehicle is designed with
headlights, front running, side marker and blinker bulbs.
Step 27 - Designed as an electrical storage devise
the automotive battery is responsible for delivering electrical power when
the engine is not in operation. All batteries possess a negative (ground) and positive
(power) attribute of and electrical element.
Step 28 - The negative side of the
is connected to the body,
and engine block of the vehicle which acts as a connector for the positive battery
power completing the electrical circuit.
Each vehicle has many fuses that are necessary to safeguard electrical circuits.
A fuse is designed to short stopping the voltage flow in the event of a power overload
or short circuit. Electrical or wire connectors can vary from a single connector
to many wires depending on the application. When performing repairs a wiring schematic
is sometimes necessary to trace wires and locate the short too be repaired. Wire
and connectors vary in size due to different amperage loads for each application.
High amperage circuits are designed with larger components to handle the load without
Common maintenance suggests inspecting electrical connectors that are visible
including the battery cables. These connections should be free of corrosion and
rust as contaminates hinder the proper operation of electrical circuits. A periodic
inspection and test of the battery
Negative Ground Circuit Connections
is necessary to avoid roadside failures. Battery terminals can develop corrosion
due to the flow of ions,
terminal and cable
cleaning is necessary to remedy this condition.
The most common problem with an electrical system is a short circuit which is
caused when a wire has rubbed through to ground or an electric motor has shorted
can cause strange problems due to insufficient operating voltage which can cause
numerous problems. Because of the nature of wiring connectors they can cause high
resistance which causes heat, allowing the connector to short and not allow the
circuit to function.
Article first published 2016-02-04