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Motorcycle Relay Devices

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Motorcycle Relay Introduction

This is the ultimate guide to the amazing motorcycle relay and it’s many applications.

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

Thinking of sourcing a new relay?

Start with the basics. Skip out the waffle.

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

adjustable motorcycle indicator relay
A photograph of an adjustable motorcycle indicator relay

Using a small signal to switch a big load….

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 the motorcycle relay down to its basic engineering principles.

Wrapping up each principle into an everyday system that does exactly what a relay needs to do…

“Using a small signal to switch a big load.”

Motorcycle Relay Technical Data

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

The Basics

What is a Motorcycle Relay?

A motorcycle relay is no different to any other relay…

Using a small signal, a coil of wire is energised.

The magnetic energy then closes an electrical contact, allowing a larger signal to flow. Therefore turning the circuit on.

Lamberts Bikes, Relay Diagram

Relay Devices Simplified

Most motorcycle relays are plug & play devices. But they are not all the same.

When sourcing a new relay there are three essential things to find out first:

  • The number and type of output contacts needed.
  • The voltage rating of the input coil.
  • The current capacity (amps) of the output contact(s).

Motorcycle Relay 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:

  • Yellow or Yellow & Red = Input coil ON signal
    • from the relay switch the relay input coil
  • Red = V+
    • from the positive battery terminal via a fuse to the relay contact
  • Green = V-
    • from the relay to the negative battery terminal
  • Black = Contact outputs
    • from the relay to the output device
  • Blue or Orange = Indicator outputs
    • from the relay to the indicator switch

Of course, many manufacturers use their own wire colour scheme. Therefore we strongly advise double checking the bikes wiring diagram.

Alternatively, talk to your local auto-electrician before starting.

5 pin SPDT motorcycle relay
A photograph of a 5 pin SPDT motorcycle relay

Motorcycle Relay Wiring Basics

The following list shows the basic connections of a motorcycle relay:

  • Input coil (switch voltage & ground)
  • Output contact(s)
Input coil

The input coil connections are used to turn on the relay. When voltage is applied the output contact(s) switch.

Connect one input contact to a switch that will be used to activate the relay.

Then connect the other to the opposing system voltage.

Output contacts

The output contacts can carry a much larger electrical load. Each is electrically isolated from the input coil and connections. Therefore, different voltages can be used to on the input coil and output contact(s).

Connect one to your power source.

Then use the other side of the contact to supply the device that is to be switched.


Although the principle operation of motorcycle relays are the same, there are many different specifications, formats and designs.

As always, the overall build quality of relays varies between manufacturers.

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

  1. SSR’s vs. mechanical relays
  2. Input coil voltage
  3. Number and type of output contacts
  4. Output contact(s) current capacity
  5. Mechanical dimensions
  6. Connectors
  7. Negative and positive earth wiring

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

SSR’s vs. mechanical relays

SSR stands for Solid State Relay. This informs that the relay has no moving parts.

The inputs and outputs of SSR’s are still isolated. However, the switching is carried out by electronic components.

Whereas, mechanical relays have physical moving parts. Mechanical relays are not just electronic.

Mechanical relays

In mechanical relays, the switching is carried out by an electromagnet pulling metal contacts into a desired position.

Springs are commonly used to return the contacts to the normal position. As a result, relay response time is slow.

4 wire mechanical motorcycle starter relay
A photograph of a M-type 4 wire mechanical motorcycle starter relay.
2 Pin Indicator Relay
2 Pin SSR Indicator Relay
Solid State Relays

Electronic components can switch very fast. Hence why SSR’s are commonly found in faster switching applications.

SSR’s can also be cheaper to manufacture. As a result, we find them used widely in motorcycle electrics. Most commonly as indicator relays.

Input coil voltage

Of course, SSR’s don’t have a coil across the inputs. However, SSR’s still have an input voltage rating that must be carefully considered.

  • Over voltage will cause damage to the input coil
  • Under voltage will cause switching bouncing and consequent contact damage

Always source a relay that matches your input and output voltage requirements.

Number and type of output contacts

An electrical switch is either normally open or normally closed.

‘Normal’ refers to the switches on/off position in its rest state.

For motorcycle relay devices the normal or rest position is the contact position while the relay if switched off.

normally open switch contact
A normally open switch contact (NO)
normally closed switch contact
A normally closed switch contact (NC)
  • Normally open contacts are useful for switching electrical supplies. Such as main power rails, lights and brake switches.
  • Normally closed contacts are commonly used for kill switches and alarm activation signals.

Consider the application wisely. Relays with more than one contact are available for more complex modifications.

Output contact(s) current capacity

The required current capacity of the outputs will be application dependant. Our words of wisdom would be to go bigger.

Running relays close to their capacity for extended period can reduce the overall lifespan of the contacts.

For pulsing applications, check the on and off durations in the specifications. This will give an insight into how the design will function in the real world.

‘Instantaneous current’ specifications are also useful for both pulsing and heavy load designs.

Mechanical Dimensions

2 wire 2 bolt motorcycle starter relay
A photograph of a 2 wire 2 bolt motorcycle starter relay

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

Consider these three things:

  1. The space that’s available
  2. The bolt hole dimensions
    • The gap between each bolt hole (if there’s more than one)
    • The diameter of each bolt hole
  3. The connection positions

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.

Connector Care Top Tips

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

Consequently, 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.

Negative & Positive Earth Wiring

For most motorcycles this section can be overlooked.

The bulk of motorcycles on the market are negative earth.

And motorcycle stator manufacturers have accommodated this trend nicely.

Positive Earth Wiring

For those classic renovators among us that love positive earth set ups…

You can use any mechanical relay that meets your needs.

Using SSR relays in positive earth setups is also achievable. Depending on the application, SSR’s may not function as intended so always consider how the internal circuitry will perform.

Guides to Wiring Relays

Motorcycle relays are very simple devices to wire and connect up. Follow these simple guides to get clarity before you start…

Indicator Relay Wiring Basics

Indicator relays come in two main forms. Mechanical relays and solid-state relays.

Wiring solid-state relays incorrectly can cause damage to the internal components. To avoid this, follow our easy to read electrical schematics.

To prevent the need for separate left and right indicator relays; indicator relays are often found connected inline to the indicator switch supply.

Many indicator relays have just two connections. For these inline devices, the output pulsing is taken care of by the internal electronics.

To activate the pulsing simply provide a closed circuit through the relay.

3 wire motorcycle indicator relay
A photograph of a 3 wire motorcycle indicator relay

Starter Relay Wiring Basics

Unlike indicator relays, starter relays are generally mechanical type relays. This is because of the high current loads found in starter circuits.

Electric starter motors used on motorcycles, make a high current circuit with the battery.

The purpose of starter relay is to connect and disconnect this high-power motor to the battery on demand.

CAUTION! There is a potentially fatal current flow in a starter circuit. Be confident that this one is wired up properly before testing.

4 wire motorcycle indicator relay
A photograph of a B-type 4 wire motorcycle indicator relay

Motorcycle Relay DIN Terminal Codes

The German Institute for Standardisation (DIN) created the standard DIN 72552 for the labelling of automotive electrical terminals.

Over time, this standard has been adopted industry wide. Today, almost every electrical contact on a motorcycle has been standardised with a numerical code.

5 pin motorcycle relay terminal layout
A photograph of a motorcycle starter relay.

Here’s a list of the DIN 72552 numerical codes that relate to motorcycle relay devices:

Relay coil terminal codes

  • 85 = V+
  • 86 = V-

Electrical contact terminal codes

  • 87 = contact common
  • 87a = normally open contact
  • 87b = normally closed contact

Additional relay terminal codes

  • 88 = 2nd contact common
  • 88a = 2nd normally open contact
  • 88b = 2nd normally closed contact

Motorcycle Relay Testing

Testing a relay is often straightforward. Here’s a couple of guides to walk you through how to test a motorcycle relay device…

  • Output contact testing
  • Input coil testing

Output contact testing

  1. Disconnect all output connections.
  2. Remove input voltage.
  3. Test the resistance across all normally closed output contacts.
    • For resistances greater than about 1 ohm, the contact has failed or has suffered excessive wear and tear.
      • Replace the relay.
    • Resistance values less than 1 ohm show the normally closed contact tested ok.
  4. Apply voltage to the input coil to energise the relay.
  5. Test the resistance across all normally open output contacts.
    • For resistances greater than about 1 ohm, the contact has failed or has suffered excessive wear and tear.
      • Replace the relay.
    • Resistance values less than 1 ohm show the normally open contact tested ok.

Input coil testing

Always check that the applied input voltage is enough to activate the relay. Do this by measuring the voltage drop across the input coil contacts. Then compare this to the relay specifications. If the input voltage is too low, but not by much, there’s likely to be a volt drop in the system.

Check the battery voltage before checking the associated switches, connections and wiring. Afterwards, if the relay continues to fail to switch over, replace the relay. In this case assume that the input coil has failed.

multi meter DC voltage range

It is possible to determine if the input coil wiring has gone open circuit. Which is often the result of a burn out. Simply measure the resistance of the input coil.

If it seems impossible to get a good reading, then the relay coil has failed. Measuring the specific resistance value of a relay coil will not provide readings for reference against the manufacturer’s specifications.

Consequently, due to the inductance of the relay coil, any resistance tests carried out with an everyday multimeter will provide inaccurate measurements.

Motorcycle Relay Compatibility

Here are a few things to extra points to consider regarding the cross compatibility of motorcycle relay devices.


Relays with a different input coil voltage rating are not cross compatible. 12-volt relays will only energise with a 12-volt signal.

Switching a 12V relay with a 6V signal will cause it to over overheat and fail. While using a 6V signal to switch a 12V relay will not allow the relay to switch efficiently and make a solid contact.

Even if a relay does switch with a lower than specified input voltage, the contacts may bounce. Which will generate excessive wear and tear at the point of contact. Therefore, significantly reducing the lifespan of the relay contact(s).

Electrical load and inline relays

Running relays close to their capacity for extended period can reduce the overall lifespan of the contacts. If possible, source relays with a little extra current capacity.

Inline pulsing SSR’s (Solid State Relays), such as inline indicator relays, use a capacitor to control the timing and duration of each pulse cycle. The speed of each pulse cycle is directly linked the load in the inline circuit.

The heavier the load in the circuit, the longer it takes for the capacitor inside the SSR to charge and then discharge. The inverse is therefore also true.

SSR’s & LED cycle speed

LEDs are very efficient. Swapping filament lamps for LEDs reduces the load in the indicator circuit. This means that an SSR’s timing capacitor can charge and discharge quickly, resulting a fast ‘blink’ rate.

A common problem found when upgrading motorcycle lighting. The common theme is to install resistors in the circuit to increase the load. And thus, slow down the charging and discharging of the capacitor. Resulting in a slower ‘blink’ rate.

This is counterproductive in improving efficiency. Our recommendation is to swap out the SSR for an adjustable SSR. These have a capacitor that can be adjusted with a small screwdriver at the base. Resulting in an adaptable ‘blink’ rate – problem solved.

FREE Relay Wiring Diagrams

Huge buttons to navigate to Lamberts Bikes motorcycle indicator and starter relay wiring diagrams. Download them direct to your device or view them online!

Indicator Relay Wiring Diagram Links

2 Pin Indicator Relay Wiring Diagram

3 Wire Indicator Relay Wiring Diagram

Starter Relay Wiring Diagram Links

2 Wire 2 Bolt Starter Relay Wiring Diagram

B-Type 4 Wire Starter Relay Wiring Diagram

M-Type 4 Wire Starter Relay 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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