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Motorcycle CDI Unit

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CDI Unit Introduction

This is the ultimate guide to the modern motorcycle CDI unit.

We’ve included a whole host of learning material and educational data, to help get to grips with these apparently plug and play devices.

Thinking of sourcing a new motorcycle CDI unit?

Start with the basics. Skip out the waffle.

Find out all that you need to know before making your next purchase.

6 pin DC input motorcycle CDI unit
A photograph of a 6 pin DC input motorcycle CDI unit with GY6 connector

Storing power from the engine, ready to generate a spark…

Explanations everyone can understand. Layered into what you need to know. Before building on complexity until you’ve had enough and beyond.

We’ve even stripped down the motorcycle CDI unit to its basic engineering principles.

Wrapping up each principle into an everyday system that does exactly what a motorcycle CDI unit needs to do… “Storing power from the engine, ready to generate a spark.”

Motorcycle CDI Unit Technical Data

Browse below to find detailed, technical data about motorcycle CDI units. If you think we’re missing something get in touch and we can publish it here for everyone to see.

The Basics

Motorcycle CDI Units Simplified

Most motorcycle CDI units are plug & play devices. But they are not all the same!

When sourcing a new CDI unit there are five essential things to find out first:

  1. Number of wires
  2. Connector type needed
  3. The power supply type (AC or DC)
  4. Desired RPM limit
  5. Timing advance curve

CDI Unit Wiring Basics

CDI units come in many different formats. The most important thing to remember is that AC input CDI units take their power supply from the engines stator. Whereas DC input CDI units take their power supply from the motorcycle battery.

CDI Unit Standard Wire Colours

Most manufacturers have adopted subtle variations of Honda 1970’s classic motorcycles. Becoming widespread these are now the most commonly used wire colours:

  • Red or Red & Black = AC Power Supply Input
    • from the stator to the CDI
  • Green = V-
    • from the CDI to the engine ground
  • Blue or Blue & Yellow or Blue & White = Trigger
    • from the pickup coil to the to the CDI
  • Yellow = Ignition Coil HV Output
    • from the CDI to the ignition coil
  • Black or Black & White = Kill Switch
    • from the CDI to a kill switch

Of course, not all manufacturers use these same wire colours. Especially in their wiring looms. It is highly advisable to cross reference your bikes wiring manual.

Alternatively, talk to your local auto-electrician before starting. However, the majority of aftermarket wired CDI units have adopted these same wire colours.

CDI Standard Pin Layouts

Check out our electrical wiring diagrams for the generic pin layout configuration of each CDI unit connector type.

Some manufacturers may design their own components to their own specifications. Therefore, always check the wiring carefully. It’s always best to trace wires back to their source.


Although the principle operation of CDI unit devices is the same, there are many different specifications, formats and designs.

As always, the internal electronics and overall build quality of motorcycle CDI units varies between manufacturers.

Therefore, when sourcing a new regulator rectifier, it’s important to consider evaluating the following before diving straight in:

  1. Power supply type
  2. RPM limiter
  3. Timing advance curve
  4. Mechanical dimensions
  5. Connectors

Continue to read the sections below to gain a more detailed understanding…

Power Supply Type

DC Supply

A DC CDI unit requires a Direct Current electrical input. This is normally supplied from the motorcycles on board 12 Volt battery.

AC Supply

An AC CDI unit requires an Analog Current electrical input. This is normally supplied from the motorcycles stator coils. The electronic circuitry of AC and DC input CDI units is very different.

DC CDI units require many more components, so they are larger in size.

Connecting the wrong supply type to a CDI will cause irreparable damage.

RPM Limiter

Many motorcycle CDI units have a built in RPM limiter to prevent damage caused by the engine revving to high.

It’s important to match this to the motorcycles engine specifications to ensure smooth running and prevent engine damage.

However, there are racing CDI units available on the market that do not have a built in RPM limiter. Use these at your own risk.

Timing Advance Curve

This is where it gets technical…

Timing advance is required in some applications to ensure that the engine runs smooth throughout its rev range.

Our best advice is to check the owner’s manual of the motorcycle engine and reference the ignition specifications.

Mechanical Dimensions

Getting the dimensions right when buying a new CDI unit will save you whole lot of headache when it comes to installation.

Consider these two things:

  1. The space that is available
  2. The type of fitting
    • Bolt hole
    • Rubber strap

It’s also wise to check the length of cable that’s available on your loom. Just to make sure that it will reach.


Unless you plan on crafting your own electrical connections this can make sourcing a replacement rather problematic.

CDI units are commonly found with one of the following connector types:

6 way 2.8mm connector

(also known as the 6 pin)

3 way and 4 way 2.8mm connector

(also known as CG style)

2 way and 4 way 2.3mm connector

(also known as GY6 style)

Connector Care Top Tips

Most motorcycle connectors have replaceable terminal pins. This means that the pins can be relocated in the connector housing.

So, there’s no need to worry don’t worry about wire positioning in connectors. This can be remedied easily with a sewing needle at home…

  1. Lightly bend down the latch on the terminal pin to remove it from its connector housing.
  2. Then, make sure that the latch is still in good condition, before finally clicking it into the location you need.

FREE CDI Unit Wiring Diagrams

Huge buttons to navigate to Lamberts Bikes motorcycle CDI unit wiring diagrams. Download them direct to your device or view them online!

We’ve categorized all our CDI unit wiring diagrams into AC and DC systems…

AC CDI Unit Wiring Diagram Links

5 pin

6 pin

5 Pin AC CDI Unit Wiring Diagram

6 Pin AC CDI Unit Wiring Diagram

DC CDI unit Wiring Diagram Links

4 pin

6 pin

4 Pin DC CDI Unit Wiring Diagram

6 Pin DC CDI Unit Wiring Diagram

Learn more…

To learn even more about your motorbikes power circuit, view “how do regulator rectifiers work?

Don’t miss our motorcycle parts knowledge database!

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2 Responses

  1. Rick crabtree

    I like the way you make things understanding and complete the explanation of how things work

  2. paul

    good day! i just wanna ask where could i get a kill switch out from DC CDI or battery operated 4 pins cdi..thanks and more power..

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