Below is a simple guide to what some of the symbols mean on the circuit diagrams. For some
of the symbols there are descriptions as to how they function. This is not a comprehensive
guide by all means but just refers to the most common symbols.
WIRES
The wires vary in size to allow different current to be carried. For example a wire with a
diameter of 0.50mm (This is the diameter of all the copper strands together) will carry 11
amps whilst a wire with a diameter of 2.00mm will carry 25 amps.
Wire no. in harness,Colour,Size (Dia of copper strands)
173,WR,2.0
TWISTED WIRES
The ‘Figure of 8’ shown on circuits as below denotes this and shows the wires that are twisted
together. A wire generates a certain amount of ‘electrical noise’ when a current is passed
through it. By twisting the 2 wires together the ‘electrical noise’ is cancelled out on each wire
by the opposing wire. This is used more on sensors and audio speakers.
Wire no. in harness,Colour,MAP (Defines twisted),What wires are in the pair, Size (Dia of
copper strands)
908,GU,MAPM05
SCREENED & TWISTED SCREENED WIRES
The ‘Figure of 8’ shown on the circuits as below denotes this and shows the wires that are
twisted together. A wire generates a certain amount of ‘electrical noise’ when a current is
passed through it. By twisting the 2 wires together the ‘electrical noise’ is cancelled out on
each wire by the opposing wire. The twisting removes internal generated noise.
The signals through a wire can be affected by externally generated electrical noise. To reduce
the interference the wires are placed inside a conductive sleeve. One end of the conductive
sleeve is always open whilst the other end can be terminated to a ground, to a component, or
left open.
The symbol for the screen is an oval with the wires that are to be screened inside it. The
letters ‘SCR’ define the screen.
908,U,MABC05
Wire no. in harness, Colour, MAB (Defines Screened),What wires are in screen, Size (Dia of
copper strands)
This defines the open end of screen.
CAN – HIGH SPEED AND LOW SPEED
‘CAN’ stands for Controller Area Network and is the intelligent wiring of the vehicle. This
wiring carries the electronic data around the vehicle allowing the various modules and
components to interrogate the network and remove their specific data signals.
There are 2 different speeds of network. A low speed that transmits at 125,000 bits per
second and a high speed that transmits at 500,000 bits per second. An analogue phone
modem is approximately 56,000 bits per second so it gives an idea of transmission speed.
The low speed network is mainly for body controller systems such as seats and doors whilst
the high-speed network is for engine management and powertrain associated systems such
as ABS.
All wiring in the CAN is twisted so the above naming convention applies. The twisted wires
always consist of one wire with a black trace in it for the negative side and one with a brown
trace in it for the positive.
High Speed CAN wire
Low Speed CAN wire
The symbol below shows a module or component connector with the pin numbers that have
CAN wires coming from them.
Where ‘CAN LS-‘ refers to a Low Speed CAN Negative Side, this naming applies to the
positive side and to the High Speed CAN.
To aid identification of the different speed CAN’s in the car different colours of wire have been
used, for example the Low Speed Volcano is GB twisted with GN, the High Speed Volcano is
RB twisted with RN.
There is attached on a separate page a list for wire colour abbreviations and what colour they
refer to.
FIBRE OPTIC
A fibre optic carries out a similar function to that of a wire in that it transmits data signals. The
differences being that where a wire is made up of copper strands in an insulated sleeve a
fibre optic is a plastic tube with a highly polished reflective inside surface.
The fibre optic carries the data in the form of a pulse of light, which is sent via an infrared
transmitter and picked up at the next component in the loop via an infrared receiver. The light
pulse is then converted to an electrical signal that is used by that module or component.
The CAN sends signals around the vehicle where the modules or components remove their
specific signals. The fibre optic is in a loop with the module components in that loop, one fibre
goes in and one fibre goes out. This is shown below with the arrows.
1,FO
Fibre Optic number in harness, Abbreviation for Fibre Optic
CONNECTORS
There are 2 types of interconnect shown on the circuits; these are shown below. Each
connector is given a dedicated C number. The number after the dash is the pin number, also
known as the cavity number. The example below is C0582 that when checked on the
attached list refers to the CEM CONNECTOR COCKPIT 2 (C3).
C0582-9
Connector C number, Connector pin / cavity number
st
The 1
type is shown for a connector that is on a module or component with a mating
harness connector attached to it.
The Module mating connector on the harness
The Module connector built into theunit
The 2nd type is shown for a connector on a harness with the mating connector on another
harness. This is known as an Inline. Again the above naming convention applies.
Cabin-Boot harness inline connectors
The terminals that are in a connector housing can have a special coating on them. This
coating if required is selected using the following criteria.
• A specific coating requested by component / system owner.
Or
• The current passing through the terminal.
• The environment the connector is to be situated with respect to temperature.
• The open circuit voltage passing through the terminal at a given.
Depending on the above criteria the coating if required can either be gold, silver, phosphor
bronze. Generally tin is the common plating on the terminals but there are some that are gold.
These are identified in the circuits with the letter ‘G’ which stands for gold after the connector
number. An example of this is shown below.
SPLICES
A splice is used where more than 2 wire that have the same requirement i.e. they need the
same signal meet in the same harness. In the example below the Front Position Lamp-LH
and Front Sidemarker-LH require the same output signal from the Central Electronic Module.
Therefore the 2 wires for the lamps are spliced into the output wire from the Central Electronic
Module on the Forward Harness.
Splice Number, Associated Name, Harness that splice is on
SPL1-FLL/FOR
Some splices appear on pages as a wire that goes to one spot and seems to terminate in
space. An example of this is ahown below.
Page splice originates on Originating page
Pages splice is on
There is attached on a separate page a list for splice abbreviations and what harness they
refer to.
RELAYS
Another significant component in the circuits is a relay, this is in simple terms a switch that
operates on the principal of electromagnetism. Below is the circuit symbol for a typical relay.
The relay shown below is a normally open relay in its inoperative state i.e The arm is in the
open position.
Relays can have either 4 or 5 terminals on the there base with the circuit of the relay on the
base or the side of the housing. There are 2 types of numbering convention for the relay
terminals, both of which are shown below.
Below is a circuit diagram to show the function and operation of a relay in a simple circuit.
(The red arrows indicate the current flow)
The current from a battery for example flows through the wires to the high power normally
open switch (The arm between pins 30 & 87A) and the low power coil (The box between pins
85 & 86). As you can see in the example above the lamp is in not illuminated, this is due to
the switch being open.
For the relay to operate there needs to be current flow through the low power coil i.e Current
in to the coil then through to an earth. How it works is that current passes through the relay
coil and creates a magnetic field, this magnetic field is strong enough to ‘grab’ the high power
normally open switch.
The magnetic field pulls the switch from it’s normally open contact to a normally closed
contact. The normally closed contact has a path to an earth, in this case it goes through a
lamp.
The high power current then flows through the high power normally open switch through the
lamp and then to an earth. This can be seen more clearly in the diagram below.
Lamp Illuminates
(The red arrows indicate the current flow)
(The yellow rings indicate the magnetic field generated)
BUSBAR
A busbar is where a electrical supply is fed into a conductive bar, wire, pcb track or whatever
it is and various modules or components ‘tap’ into this busbar to draw there required power.
The Central Electronic Module has 4 of these busbars internally, each of which is supplied
from an external power supply, that supply can be a battery feed, ignition feed or a switched
supply.
One of the 4 inputs to abusbar Some outputs that tap into Busbar 3
The symbol shown below is the symbol used on the circuits for a busbar, the number inside
the box refers to what busbar it is in the Central Electronic Module.
FUSE
A fuse is a device used to protect a module or component from excessive electrical current
which can cause damage or destroy that module or component. In practice the fuse is placed
in between the power source and the module or component that is being protected.
The size or ‘Rating’ of the fuse in amps is calculated according to the power requirements of
the module or component it is protecting with other factors being taken into consideration. If
the rating has been calculated correctly then the fuse when excessive current passes through
it will ‘blow’ before any harm or permanent damage occurs on the module or component it is
protecting.
An example of this is shown on the next page.
Lamp has blown due to excessive current flow
(The red arrows indicate the current flow)
The diagram below has the fuse placed ‘Inline’ between the power source in this case the
battery and the lamp.
Fuse has blown due to excessive current flow but not the lamp
Below is the circuit that are shown on the attached circuit diagrams. The number above the
fuse symbol is the fuse number; allocated to this fuse in the Central Electronic Module is the
number 59. The number below the fuse symbol is the rating.
RESISTOR
A resistor is an electronic component that by way of its construction reduces the current
flowing through it. A resistors unit of measure is the Ohm; the symbol for this is ‘Ω’.
The diagrams below show a resistor and a variable resistor.
12 Volts, 10 Amps in 12 Volts, 0.021 Amps out
(The red arrows indicate the current flow)
A variable resistor works in the same manner as a normal resistor but the resistance values
can fluctuate. The construction of a variable resistor depends upon its use and environment.
One example is for the fuel tank level sensor. The sensor sits in the fuel tank and the
resistance in the sensor varies according on the amount of fuel in the tank. This is all down to
the reaction between the liquid and the materials in the sensor.
The variable resistor can work using light, temperature, pressure to name but a few to change
the resistance. It is all down again to construction and environment. On the next page is an
example of a variable resisitor in a fuel tank level sensor. The tank full level is 10 ohms and
the tank empty level is 204 ohms, the resistance will vary between 10 and 204 ohms
depending on how fuel is in the tank.
12 Volts, 10 Amps in 12 Volts, Tank Full = 1.2 Amps out
12 Volts, Tank Empty = 0.058 Amps out
(The red arrows indicate the current flow)
LAMP
This is self-explanatory as it refers to a light bulb. Below is the symbol for a light bulb, shown
below the symbol is the power of the light bulb in watts.
SWITCH
This is self-explanatory. There are numerous of types of switch, a couple of examples are
shown below as a rough guide.
3 Position Switch2 Position SwitchNormally Open Switch
MOTOR / PUMP
This is self-explanatory. It is the same symbol for a pump or a motor it’s just the description
differentiates them.
DIODE
The simplest way of describing a diode is ‘a non return valve’. The current will flow through
the diode from the anode to the cathode, due to the construction of it though current cannot
come back. Diodes are used to reduce the possibilities of ‘back feed’. This is where current
comes through the circuit the wrong way for one reason or another. Below is the circuit
symbol for a diode.
Anode Cathode
(The red arrows indicate the current flow)
LIGHT EMITTING DIODE
The light emitting diode works on the same principal as the diode. The main difference is that
in the manufacturing process one of the materials is replaced by another. This replacement
material has certain properties that when a certain voltage passes through glow.
Arrows that show it’s an LED
Anode Cathode
Colour
(The red arrows indicate the current flow)
TRANSISTOR
A transistor in simplistic terms is a switch with no moving parts. The ‘switching’ is controlled
by electronics and currents etc rather than a physical switch being operated.
Here is the circuit symbol for it. The example shown below is one of the most common basic
type used called a ‘Bipolar’.
FET (FIELD EFFECT TRANSISTOR)
A field effect transistor is again in simplistic terms a switch with no moving parts. The
‘switching’ is controlled by electronics and currents etc rather than a physical switch being
operated. The main difference between this and the type of transistor shown above is this one
operates using a magnetic field.
Here is the circuit symbol for it.
EARTH / GROUND (THE VERY IMPORTANT BIT)
For an electrical current to ‘flow’ around a circuit it has to start from a power source and go to
an earth / ground. If there are any breaks in this circuit then current will not flow, this is called
an ‘Open circuit’
The example below will demonstrate this.
The lamp does not illuminate as there is no earth / ground.
Earth Braid from Battery
Main Earth Point
(In this case the car body)
(The red arrows indicate the current flow)
The example below shows what happens when you put the other side of the lamp to the earth
/ ground and complete the circuit. As you can see the lamp illuminates.
Earth Braid from Battery
Earth Point
(In this case the car body)
Main Earth Point
(In this case the car body)
(The red arrows indicate the current flow)
The flow can be interrupted or controlled by various means such as switches, relays etc. A
switched sample is shown below. Lamp not illuminated as no ground path as switch is open
Earth Braid from Battery
Earth Point
(In this case the car body)
Main Earth Point
(In this case the car body)
(The red arrows indicate the current flow)
Lamp illuminates to ground path now switch is closed
Earth Braid from Battery
Earth Point
(In this case the car body)
Main Earth Point
(In this case the car body)
(The red arrows indicate the current flow)
There are 2 types of earth, Signal Earth and Chassis Earth, these are referred to sometimes
as a Quiet Earth and Noisy Earth respectively.
Some sensors for example specify a Signal / Quiet Earth. While components such as pumps
and motors can have a Chassis / Noisy Earth. The reason behind this is that pumps, motors
and the like can generate ‘electrical noise’ by the way of there operation. Some of this
‘electrical noise can be transferred through wires, it is this ‘electrical noise’ can have an
adverse effect on sensor signals and affect the readings they back.
Keeping Signal / Quiet and Chassis / Noisy earths separate reduces the effect of ‘electrical
noise’ being transferred from component to component.
This symbol is a standard symbol for earths.
On the attached circuit diagrams earths are shown as eyelets with the description of Earth**** next to it, the earths also comply with the 4 digit C number. An example of this is shown.