Tech Tip: Lucas 30608 Ignition Switch - Understanding 3 & 4 Spade Terminals

Tech Tip: Lucas 30608 Ignition Switch - Understanding 3 & 4 Spade Terminals

At some point during your ownership of a vintage motorcycle you may encounter that your original Lucas ignition switch may need to be replaced

Usually a failed ignition switch is caused by vibration, moisture and from "installing / removing" your ignition keys "in and out" over the years which will eventually wear your tumblers

If you wait long enough to replace a known bad or failing ignition switch, you may find yourself stranded on the side of the road! 

Although most know the basic function of the Lucas 30608 ignition switch, some folks are not aware that the new Lucas and EMGO 30608 ignition switches are slightly different from original Lucas switches 

If you are in need of a replacement ignition switch or you already have a replacement switch on hand from us you may find that your spades have a different terminal count and may confuse you

In today's Tech Tip post we will cover the main differences from original and new switches on the market

Keep reading the post below and follow along! 


The switches 


Before we dive into this topic, lets showcase 3 Lucas 30608 ignition switches commonly found on most late model Triumph, BSA and Norton marks along with vintage British vehicles from approx 1966 and later..


3 Lucas 30608 Switch - Original, Lucas & EMGO

 Original and new Lucas / EMGO switches 

Above we have 3 types of Lucas 30608 ignition switches


From left to right 

  • Left (original Lucas) - 3 prong
  • Middle (new Lucas) - 4 prong
  • Right (EMGO) - 4 prong


As you can see all the switches look fairly the same minus the style of key head, finish, etc

The main feature most noticeable when installing a new Lucas or EMGO switch is that there are 4 spade / prong's rather than 3 spades like the original Lucas switches as shown above in the far left..

For the most part, all new Lucas and EMGO ignition switches will replace Lucas 30608 and also other associated old and new superseded part numbers ...


Common part numbers

Since the Lucas 30608 switch is common on most models the "new" Lucas and EMGO switches will replace some of the following original parts numbers..


  • 19-1775
  • 99-0558
  • 31899
  • 03-3016
  • 31886
  • 60-0989

 I'm sure there are more part numbers out there, above is just a small few (you get the idea)

Spades / terminals 


The main question that we get from customers when replacing an old Lucas ignition switch with a new Lucas or EMGO switch is:


  • "I purchased a new Lucas 30608 switch and noticed it has 4 prongs and not 3 like my original, will it make a difference?"
  •  "What does the 4th prong do that my original Lucas switch did not have?"
  • "Do I need to send this switch back for a 3-prong switch?"
  • "Which spade do I hook my wires up to?"


 To answer your question in a straightforward manner the answer is the new 4-prong 30608 switch will work and replace all 3-prong ignition switches

Both units (3 and 4-prong) feature a 2 position setting.. “on and off” as fitted to most models from approx 1966 and on

 The reason why Lucas and EMGO brands are producing a 4-prong switch is for "universal" applications 

It is more efficient to produce 1 switch to replace 5 or 6 variations that where used over the years rather than making 5 or 6 difference switches when in reality they are all same 

In other words, the 4-prong ignition switch is a better choice and replacement part 


Numbering Of Switch Terminals #1-3

 Each terminal numbered 


If you have an original Lucas switch for reference (and replacement) you can mark each terminal #1, #2 and #3 and simply transfer your old wires to the new 4 prong switch in the same sequence

Internally the switches are same, so don't let the 4th prong confuse you!

Most motorcycles do not use the 4th spade terminal so you can leave it "as is" or simply put a cap or block on the end of the spade (your choice) 


Multimeter Testing On Lucas 30608 Switch

If you do not have an original switch to copy, get out your multimeter in the ohms setting and start checking continuity between each spade terminal to figure out which wire belongs in the proper location


Need a new ignition switch?

Lucas & EMGO 30608 Switches For Sale

Should you have an original Lucas switch that needs to replaced we have 2 new types of complete ignition switches that are ready to be installed 

Click on the links below to purchase your new switch 

 Part Type  Brand Part Number Terminals Link
Ignition switch (complete) Genuine Lucas 30608 &  4 Click Here
Ignition switch (complete)
EMGO (Taiwan) 30608 &  4 Click Here




 The next time you are in need for a replacement igniting switch do not let the 4th terminal trick you!

It's the same switch with an added terminal for "other" applications 

Install the switch as per your wiring diagram or how your machine was originally wired and all will work and function well


Thanks for reading

If you've enjoyed today’s Tech Tip post then we have more parts for you which can be found in our online archive

Click here to view our blog and Tech posts archive 

If you have any questions please let us know by commenting in the section below 

Ride safe! - Classic British Spares


  • IanJ

    I discovered this article a couple of days ago, and it made me curious when I found Bryan Vandiver’s August 03, 2019 comments about what appeared to be leakage or a ground fault in the switch. I have an EMGO and an old Lucas switch, so I decided to perform some experiments and disassembled both.

    First, I found the actual switching components to be so close to identical that I was able to mix-and-match them while testing and found no significant difference in terms of their respective electrical properties.

    Using a multimeter, I first tested resistance and found both of my switches to read zero ohms with the 200-ohm setting selected. After mixing the components, I got the same readings on both switches.

    I then hooked one pin to a battery reading 12.67 VDC and set my scale to 200 Mv, the most sensitive my multimeter is capable of. The readings on both switches consistently read 13.6 mV and within seconds degraded to 9.6 mV. This was the case whether using the components original to each switch of several mixes of components between the switches.

    The low readings suggest to me that any perceived leakage is probably the result of the dielectric properties of the insulator to which the lugs are attached. The fact that all of the actual switching components are so physically and electrically similar is remarkable and speaks to EMGO’s quality and faithfulness to the Lucas design.

    It would be interesting to see if I can reproduce Bryan’s experience in a few weeks when I have my machine fully reassembled and powered up.

  • Gregory Bates

    Lot of help
    Thanks alot
    Works great

  • Bryan Vandiver

    I recently replace the ignition switch with a 4 proged lucas, on a 1976 t140v triumph, and in the process noticed something that was kinda troubling. The body of the case/outside of the swich is ‘energized’ when switched on (tested with an vom). This is not really an issue for a ‘positive ground’ bike, but could be potentially hazardous for a bike that has been converted to negative ground. I had converted my bike to negative ground, along with installing a podtronics, and Pazon ignition. Fortunately, the switch is wrapped in electrical tape, and there is a fibre washer under the switch mounting nut, which seems to isolate the switch from ground. I notice the problem while testing the keys in the switch, and one of the keys on the key ring had swung up , and hit the turn signal stem, and it sparked when it hit the stem. Anyone who is converting to negative gound should be aware of the issue, and make sure the ignition switch is insulated from the chassis.

  • Bob Middleton

    Thanks for the tip.

  • Classic British Spares

    @Bob – thank you Bob. To answer your question, if you take a meter and measure each terminal and you find #3 and #4 the same, it will not do any harm to use either of the terminals. It’s also nice to have another terminal available for other purposes

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