Motorcycle Wiring - A Basic Guide !

[Coconut]

DISCLAIMER :
I AM NOT A QUALIFIED AUTO ELECTRICIAN !
THE BELOW INFORMATION IS PROVIDED FOR INFORMATION ONLY, TO ASSIST
THE READER IN GAINING A BASIC UNDERSTANDING OF ELECTRICAL CIRCUITS,
AND TO HELP IN IDENTIFYING FAULTS – TO BE USED AT YOUR OWN RISK ! 

A lot of questions crop up on the Forum about Bike electrics,
where the person enquiring has very little electrical knowledge,
so I’ve put together this BASIC guide - which will hopefully help to
explain how some things work, and why they sometimes don’t !   



The Trophy has a fairly typical 12 Volt DIRECT CURRENT ( or D.C. ) system
with NEGATIVE EARTH ( or Negative Ground ).
The Main 12 Volt Battery is located under the cover below the
right handlebar grip and has a POSITIVE and a NEGATIVE Terminal. 

POSITIVE is sometimes referred to as +ve, or +, or Supply, and
NEGATIVE is sometimes referred to as -ve, or -, or Earth, or Ground.

A CIRCUIT generally begins and ends at the Power Source ( usually the Main Battery ),
and comprises all of the wires and individual parts ( Components ) to complete the Circuit.

A COMPONENT is an individual part of a Circuit, such as a Battery, Wire, Switch, Bulb, etc.

In a Direct Current ( D.C. ) system, CURRENT can be considered to "flow" from the Positive Side
of the Battery through the Circuit and then to the Negative side, ( usually ) along a wire or wires.

CURRENT is expressed ( measured ) in Amperes, or Amps ( A ). 

The rate at which the electrical POWER is "used", is expressed in WATTS ( W ) ,
e.g. a Headlamp bulb might "use" 55W, whereas a lower powered Tail Light bulb may be 5W.

Components with higher Wattages draw more Current.

There is a mathematical formula for calculating Power ( W)  or Current ( A ).

On a motorcycle, the Voltage ( V ) remains fairly constant and is assumed to be 12V,
though in practice it is often slightly higher than this at around 13V or more.
Current ( A ) =  Power ( W ) / Voltage ( V ).

A 55W headlamp bulb would therefore draw 4.58A ( 55W / 12V),
and a 5W Tail Light bulb would draw 0.42A ( 5W / 12V).

FUSES are designed to Blow ( fail )  if their rated Current is exceeded.
This provides protection against overheating or damage to wiring and components
if the Current draw is excessive, such as in a “Short Circuit”.

Watts = Amps x Volts, so a 10A Fuse could theoretically provide 120W ( 10A x 12V ).

As Current is drawn from the Battery, the Voltage and therefore the available power,
will gradually reduce as the Battery Discharges.  To prevent this happening the Battery
needs to be Recharged and this is accomplished by an engine powered Generator,
( known as an Alternator ), which provides Power, and keeps the Battery charged
while the engine is running, or by use of an external Battery Charger,
or Battery Tender if required, e.g. when the bike is not in use for extended periods. 

Alarms, Digital clocks and similar Components use small amounts of power even
when the Ignition is switched OFF, hence the reason for using a Battery Tender.

If the Power used by those Components is not replaced, the Battery
will gradually Discharge and little or no Power will be available.
If the Battery Voltage is allowed to completely drain, it can result in damage
to the Battery, which may then need to be replaced.

WIRING
Generally, Multi stranded Copper wires are used, coated in an Insulating material.

Larger size wires ( can ) carry higher Currents, so the Main Battery Wires are much bigger
( in cross sectional diameter ) than the wires used for, e.g. a Single Indicator bulb.

To simplify matters, and reduce the amount of wires needed, the Negative Earth,
or Negative Ground system is used, where The Negative terminal of the Battery
is connected by a heavy duty wire directly to the bike Frame.

Electrical Components can than then have a single Power / Supply wire from the Battery,
and either a short(er) wire - connected directly to the Frame, or the metal body
of some components may be attached directly to the frame to complete the Circuit.
 
The Power / Supply wire is usually provided via a Fusebox, containing Fuses
of appropriate ratings, to protect the various Circuits.

Individual Wires are colour coded, to help identify them and match up with Wiring Diagrams.

Due to the limitations of the number of colours available, wires may have
an additional coloured stripe along their length, e.g. a Red wire with a White Stripe.

Wiring diagrams use pictorial representations for the various Components,
and are often printed in Colour, but are also tagged with abbreviations of their colours,
where the main colour is shown first, followed by the colour of any stripe.

e.g. R is a Red wire, and RW is a Red wire with a White Stripe.

There is usually a Key to these colour abbreviations, which, on the Trophy are :

• B = Black
• U = Blue
• N = Brown
• G = Green
• S = Slate / Grey
• O = Orange
• K = Pink
• R = Red
• P = Purple
• W = White
• Y = Yellow
• LG = Light Green
• LU = Light Blue

Individual components are usually drawn on Circuit diagrams to help explain
their meaning and operation, a good example being a basic switch :

Switch in OFF Position:


Here are some of the other Pictorial representations used on the Trophy Wiring Diagram :

BATTERY – The motorcycle main 12 Volt Battery -
showing Wiring Colours ( N = Brown, B = Black ) :



BULB – A variety of traditional Tungsten Single filament bulbs are used
for the Front Position Light, Front and Rear Indicators, etc :

 
The Headlight bulbs are “Twin Filament”
for the Main and Low / or “Dipped” Beams :


ECU / ECM – Electronic Control Unit, or Electronic Control Module. 
These contain complicated electronic circuit boards for various purposes including control
of the Ignition Timing, Immobiliser and Tyre Pressure Monitoring etc. 
To avoid the risk of causing damage it is usually recommended to disconnect the main Battery
when carrying out any work on, or inspection of their electrical circuits.
The internal circuitry of such ECU's are not usually shown on a Wiring Diagram.

GROUND / EARTH CONNECTION - Connection to the motorcycle Frame,
or other component, that in turn is connected to the Negative Battery Terminal :


MOTOR – A device that provides a turning motion when power is applied. 
The rotating shaft of the motor usually has some sort of mechanical link
or cogs / gears etc. as in the Windscreen motor, Headlamp level motor and TES motors :


PHYSICAL WIRE CONNECTOR - These may not be obvious as they can be taped up
and buried inside a section of wiring harness. 
Here, 4 wires are shown joined together :


NOTE : Wires shown crossing on a Wiring diagram, WITHOUT a Connector as shown above,
are NOT connected together at the point(s) where they are shown crossing :


PLUG / SOCKET CONNECTOR - Showing the number of Pins, and the Pin numbers :


RELAY – A Heavy Duty Switch used to switch Components drawing higher levels of Power,
for example Accessory Sockets into which Heated Gear might be connected, and / or for 
specific wiring solutions such as the Changeover Relays used for the electric screen.
The Starter Solenoid is simply a bigger version of a Relay.
Here the Relay Coil - at the bottom of the Image, when energised -
usually by Power being provided when a Switch is turned to ON,
causes the Relay Contacts - at the top of the Image, to close,
completing / turning ON the circuit :

 
SWITCH :
A single switch housing may incorporate multiple switches. 
The wiring diagram will usually show the individual switch contacts.
Here, Switch 1 is a simple One Way ON / OFF Switch, and Switch 2
is a 2 Way ( 2 outputs ) Switch, both inside one Switch Housing :

 


TESTING.
Basic testing of electrical circuits is within the capability of most home mechanics,
and can be broadly split into three categories :

• Integrity : Checking that the physical contacts at each end of the wire
  are sound, e.g at the Switch contacts, and any Multi-Plug connectors
  into which the Component may be connected
• Continuity : Checking that there are no breaks in the length of a wire
  e.g. from the Switch to the Component
• Short Circuit – checking that a circuit providing power to a Component
  is not being unintentionally diverted to Ground, e.g. a “live” wire chafed through
  and coming into contact with the Frame causing the fuse for that circuit to blow.

There are numerous methods of checking electrical circuits, including a simple Bulbholder,
or Induction type testers that can find broken wires. 

My personal preference is for a "Multi Meter", having the capability to measure
in the region of 12 Volts D.C. and Resistance ( measured in Ohms ) for checking Continuity.

Multimeters need not be expensive, there are many types available at low cost,
with numerous Videos and tutorials on YouTube etc on how to use them :


Care must be taken when using the Continuity Tester NOT to connect the Meter to Live wires,
which could cause damage to the Meter.

When testing wires to or from an ECU, disconnect the Main Battery AND any wiring at the ECU.

NOTE : It is NOT recommended to use a Multimeter for checking MAINS Power circuits,
such as those found in your home running at 230V ( or 110V outside the UK etc ),
UNLESS you are properly qualified to do so, as serious Injury or Death is a real possibility !



Here is a simple example of a Switched, Fused, Lighting circuit :


Let us imagine that the Bulb does not illuminate when the switch is operated,
and we want to find out why.

The possible causes are :

• The Bulb has failed
• Main Battery is discharged
• The Fuse has Blown
• The Switch is faulty
• There is a break in continuity from the Battery +ve to the Bulb
• There is a break in continuity from the Bulb to Battery -ve ( via Ground )
• There are poor / broken connections at the Battery, Fuse holder,
  Switch, Bulb holder, or Bulb Contacts.
• There is a Short Circuit somewhere between the Input connection for the Bulb, and Ground.

While this may appear complicated, and the below steps seem lengthy, it is quite easy to Test.

Experience will indicate that the most likely cause, and often the easiest to check,
is a failed Bulb, so check that first - simply try replacing with a known Good Bulb, 
or test with the Multi Meter by removing the Bulb and checking for continuity
between the bulb contacts, one of which may be the Bulb Body.

If the Bulb is good – check its contacts, and that the contacts inside the Bulb holder
are clean with no signs of corrosion.

Similarly test the Fuse – If it has blown replace with one of the same rating,
and check the contacts inside the fuse holder are clean and not corroded.
 
If the Fuse blows again as soon as the switch is turned ON,
this indicates a likely Short Circuit. ( See below ).

Once the Bulb and Fuse are known to be good, Check the Main Battery.
Do other circuits work ?
Use the Multi Meter set to measure DC in the region of 12 Volts, and check that
the Main Battery is charged – with the Red Meter Lead against the Battery + Terminal,
and the Black Meter Lead against the Battery – Terminal.

Progress along the Circuit testing for Power at the Fuse holder input AND output terminals,
then the same at the Switch ( ensuring the Switch is ON ), and then on to the Bulb holder.

If at any point there is NO Power, this indicates a break in the preceding wire, or poor connection(s).
If Power is present at the Bulb holder, check Continuity from the Output side of the Bulb holder to Ground,
to identify any poor connection or broken wire.

To check for a short circuit, e.g. if the Fuse continually blows, disconnect the Battery +ve terminal,
and remove the Bulb from the Bulb holder, then use the Multi Meter to check at each point of the circuit.
There should be NO Continuity to Ground from :

• The wire removed from the Battery + Terminal
• The Fuse holder input and output Terminals
• The Switch Input and Output Terminals
• The Bulb holder Input Terminal

If Continuity IS found, try to isolate it, for example remove the Fuse and check if the Short Circuit
is on the Input side – indicating the problem lies with the wire from the Battery,
or the Output side indicating the fault lies after the Fuse holder, and so on. 

When the section with the Short Circuit is identified, examine that section of wire
to find where it is shorting out to Ground – look for signs of chafing against other wires
or parts of the frame / components of the bike, and repair when found.


These Testing principles can be used, together with the Trophy Wiring Diagram
( found in the Service Manual ), to identify most electrical faults.

Please feel free to add any helpful comments, but try and keep to the "Basic" theme !

Cheers 

[/list]

[digital]

Is a great job and very well explained (without any doubt). Taking the precautions you say well at the beginning, this tutorial can help many people.

My work is electronics and today I work in telecommunications and always learn something and serve as a reminder.

This Post deserves a pushpin.

Thanks Coconut.

[Wilko]

Well Done Coconut  , a great write up explaining the basics of fault finding, I guess that must of taken a fair bit of your time to do, so give yourself a well deserved pat on the back. 

[digital]

I've been in this forum for four years and months. The truth is that during these years I have been seeing and I am greatly surprised how a person like coconut goes out of his way and wastes a lot of his time to help people who need to know something about a TTSE.

So the pat on the back is not enough to thank you for such a great job you do without any interest.

Thanks ... coconut

    

[Coconut]

Cheers digital 

I don't consider it time wasted at all - I just like helping out when I can ! 

[Ad™]

What a great guide ! 

I've made it "sticky" - hope thats ok 

 

[digital]

Originally Posted by Coconut

Cheers digital 

I don't consider it time wasted at all - I just like helping out when I can ! 

I understand perfectly, because I also do the same as you.

[JerseyJeff]

Great post, thanks Coconut