Norton Commando Wiring Diagram

Grant Tiller

I often help people with their motorcycle wiring issues – both in ‘real life’ as well as on the Facebook groups and various forums.

I’m pretty good at wiring, and fault finding so am not scared to roll my sleeves up and get stuck in.

They say a picture paints of thousand words, so I often refer to pics when I’m trying to help someone, and Bill’s circuit diagram has proved really helpful on numerous occasions.

Over the next few days, I will be posting diagrams that have been modified to accommodate common upgrades – in particular electronic ignition and modern regulator/rectifier units.

With Bill Turnbull‘s kind permission I made some edits to his original diagram.

The wiring in these pics are as per the original, just reordered slightly, and made even easier to follow and with a few edits:

  1. indicator switch wires (GR and GW) should be routed back to the main connector block
  2. there was no color shown for the points wires – these should be BW and BY
  3. the wire from the ballast resistor and linking the two coils should be WP
  4. the pin numbering on the master switch was wrong – I think this was an error in Bill’s diagram.

Thanks to Les (L.A.B) from the Access Norton forum who helped immensely with this, and has kept me honest.

Pre-1971 (ammeter in the headlight shell and Wipac Tricon type handlebar switch) PNG 3066×1841

This diagram is also downloadable as a PDF from HERE

Grant Tiller

1971 (three wires to the master switch) PNG 3066×1841

This diagram is also downloadable as a PDF from HERE

Grant Tiller

1972 onwards (four wires to the master switch) PNG 3066×1841

This diagram is also downloadable as a PDF from HERE

Grant Tiller

On the MK3 diagrams, you will see a grey wire that goes from PIN 2 of the ignition switch (master switch) up to the right side handlebar switch. It is a hot feed to the starter button.
This was present well into MK3 production, but as Norton and Triumph models started sharing the parts bins the switch gear became common with the Triumph T140E. As a result of this, the grey wire disappeared, and the starter button was subsequently fed by the white wire that also feeds the kill switch (off/run switch)

Another element of the MK3 that sometimes causes confusion is the wiring around the Warning lights.

The factory workshop manual shows the following:

Grant Tiller

I have covered this in more detail in a separate article, which can be found here.

But in short, the cable colors used for the sub-console wiring harness were not the same all the way through MK3 production – so certainly something to watch out for!

1974 MK3 Early Bikes – there were around 2,000 bikes that were built around the December 1974 timeframe that have three additional fuses that can be found in the headlamp bucket.

These bikes are also wired with the old Lucas 3AW 3 wire ‘silver can’ assimilator.

1974 MK3 (early – three additional fuses in the headlamp shell) PNG 3066×1841

This diagram is also downloadable as a PDF from HERE

Grant Tiller

1975 MK3 this is the most common configuration, and takes us through to the final Commando that rolls off the production line.

1975 MK3 (Original) PNG 3066×1841

This diagram is also downloadable as a PDF from HERE

Grant Tiller

1975 MK3 Canadian Market – there were legal requirement in Canada around the headlamp being on while the engine was running, so the wiring diagram includes changes needed (swapping out the Warning Light Assimilator 06-6393 for the Headlamp Warning Unit 06-6392). Note that a different Master Switch is also required.

This is covered in the Factory Wiring Diagram, by notes.

1975 MK3 (Canadian Market) PNG 3066×1841

This diagram is also downloadable as a PDF from HERE

Grant Tiller


A couple of points about the way these diagrams have been drawn:

  1. The diagrams on my site are schematics – the components are not drawn in the physical location on the bike. Instead they are drawn in locations that make the diagram the easiest and most logical to follow.
  2. Where the same colour wire goes in to and out of a single connector, that connector has usually been omitted from the drawing.
    It’s obvious on the bike, is easy to spot and easy to troubleshoot.
    Leaving them off the diagrams makes them a LOT easier to read, and considerably less cluttered.
  3. Wherever the earth or ground side of a component goes back to the battery, the drawing shows a red earth symbol:
    Grant Tiller
    In reality, this could be connected either to a red wire in the bike’s wiring harness (loom) OR it could be attached to the frame or engine of the bike.

    I have shown the red earth symbol each time in order to massively simplify the diagram, and make it a lot easier to understand for everyone.

    I have also coloured them red as a gentle reminder that these bikes are wired positive earth!

Hopefully these will help someone – don’t be scared of electrics.

The trick is to not be overwhelmed, print out the diagram, and follow each line.
There is no hurry, take your time.

And if you get stuck, reach out – there are lot’s of people willing to help!

26 replies

  1. Grant,

    I’m working on a 650SS that has been converted to Boyer and Tympanium voltage regulator. The wiring is a mess and the 650SS didn’t even have a fuse or master switch. Your Pre-1971 drawing is close to how I’m going to wire it. It needs three changes other than the EI and VR. There is no front brake switch. The white wire that connects to the ammeter I’m going to connect the the switched side of the master switch. also, the white/brown wire that connects in the drawing from the un-switch side of the master switch to the headlight switch I’, also going to connect to the switched side. So, the master switch will turn the bike off completely.

    If you’re looking for something to do, it would be helpful to have a diagram to help me remember as I wire. Don’t give it a second thought it you don’t have the time.


      • Hi Grant
        I have a 1971 Commando and am trying to trace the wiring and am finding that my loom does not fit either of the wiring diagrams shown.
        It seems to fit exactly as the 1971 three wire switch but mine is fitted with an ammeter so my question is, has the wiring been modified by a previous owner and how should the ammeter be connected into the circuit.
        Also when I use my indicators the ammeter shows an intermittent discharge is this correct.
        Hoping you may have time to give me an answer

        • Hi John,

          The earlier bikes with standard ammeter wiring are very very different – much simpler and with only a two position ignition switch (on or off).

          It sounds to me like a previous owner has indeed run the wires for an ammeter.
          I did a custom wiring diagram for Vaughan, a guy on facebook who has got exactly the same setup as this.
          The only difference is that his bike is a 1972 model, so has the four pin master switch.
          Have a look here:
          It maybe closer to your machine than the factory diagram!

  2. Hello Grant – I’ve a 1971 Commando & I found the wiring diagram you provided above very useful. Although my bike is a 71 – it was delivered in early January 1971, so was presumably built towards the end 1970 – although I understand from the Vintage Motorcycle Club, that the records show it was built to a 1971 spec. Despite this, the headlight is the “halo” type and has an ammeter and only 1 warning light. The wiring loom has an assimilator and a Fiamm horn & relay. Obviously not things on the wiring diagram. I’ve bought a new loom but connecting it up has not been as straightforward as I’d imagined!🤣

    I wasn’t sure if the relay was needed (the wires to the switches look to be the same thickness as the rest of the loom) despite this I tried to incorporate it but it doesn’t seem to have worked out & I’ve had difficulty finding an exact wiring diagram for the Fiamm relay. It has the usual #87 terminal (going to the horn) & the #86 is connected to the 30/51 terminal – there is another “bladed” terminal (unmarked) & a wire coming off relay (again unmarked). Have you any advice about the need for relay & assimilator & how they should be wired in?

    Thanks in advance – cheers

  3. The ammeter, red warning light and switch were in the 1968-1970 7 inch headlight.
    Confusingly the red light was for the high beam warning light!
    There was no assimilator on these bikes.

    The ammeter was dropped the following year, and three warning lights were in the headlamp shell until the MK3 850 came along.

    The fiamm horn and relay were a popular upgrade of the time – although not standard.
    The only relays used on the Commandos as standard were on the Interpols (police bikes)
    The relay pinout is pretty standard – but don’t forget on this bike you are making and breaking the earth on the handlebar switch.

    I’ll make a diagram for you – do you have any other upgrades on your bike that need to be included (electronic ignition, regulator/rectifier etc) or is is standard?

    Are you using the original tricon switch or have you fitted an aftermarket one and lost the use of the flasher button?

  4. Hello from New Zealand Grant,
    Many thanks for making these awesome wiring diagrams available!
    Have just rewired my Canadian version Mk3, after upgrading to 3 phase alternator, Trispark ign and Podtronics unit. Bought a full set of new wiring looms, unwrapped each one, removed all the redundant wires then re-wrapped.
    Just doing the headlight loom now, however all the connections are bullet connectors, whereas the original had small white plugs inside the headlight shell. I contacted the manufacturer in UK, who advised that the small plugs were causing problems for many owners, so they replaced them with bullets of which there many. I am thinking of cutting of the bullet connectors and plugs from the handle bar switches and using waterproof Deutsch style connectors. Just wondering if you have any further suggestions?
    Kind regards

    • Glad you like the site – hopefully it’s been useful during your project!

      Yes, I have heard that Autosparks (the makers of the Lucas/Wassell and the Andover Norton harnesses) have stopped supplying the correct plugs.

      This is a decent source for connectors:

      Tricor Andy Gregory is the guy that makes the Sparx aftermarket handlebar switches.

      I have also had some great luck with these guys.
      They sell replacement pins that allow you to put new cables in the original connectors:

      There’s no problem with chopping off the plugs and using standard bullet connectors instead.
      But I would recommend that you use a decent crimp tool and insertion tool if this is the route you plan to take.

      A good source for wiring bits on your side of the pond is British Wiring.
      They are based in Berks County, Pennsylvania but that’s a lot nearer to Canada, so shipping costs will be lower.

      The company was originally setup by Roger Davis, who owns Autosparks (the manufacturer of the harness)
      And although he sold the US company a few years ago, they are still Autosparks stockists and keep an excellent stock of parts.

      I use (and recommend) Deutsch connectors – they are the best quality by far versus the other multi-way connectors available.
      The slightly smaller DTM connectors can take enough current and versus something like the superseal connectors, they are a lot smaller and easier to hide away.
      The other thing I like about them is that you can disassemble the plugs and sockets which is handy if you need to pull wires through holes and grommets.

      Hope that helps!

  5. Hi Grant,
    My apologies for the late reply, just found your reply on access norton forum without any notification
    Anyway, many thanks for your reply and useful information. Have decided to use the Deutsch DT plugs, as they have 2 sizes of #16 terminals whereas the DTM plugs have only 1 size and are only rated at 7.5 amps. Having a few problems with my Sparkbright led charging indicator light. At a steady speed, it sometimes flashes red for a few seconds before going back to green again?
    Kind regards from New Zealand

    • I usually prefer the charge warning lights, as you can use the existing lamp so that everything still matches (particularly useful with the MK3)

      However, I have a couple of the Sparkbright LEDs – I have one in the toolbox, and use it as a quick test tool for battery condition (saves breaking out the multimeter)
      The other I have fitted on a cafe racer.
      I am amazed by how much difference in behaviour I see depending on how close to the battery the unit is wired.
      If it’s directly on the battery it seems far more stable than if it is at the front of the bike via several connectors and the ignition switch.
      I also notice a difference on bike wired with the blue can capacitor versus bike that have it removed – so it seems that the smoothing must make a difference to the reaction speed of the status monitor – ironing out the bumps to take away anything that may throw a sporadic status change.

      It’s no big deal, just an observation.

  6. Hi Grant
    I have a oct 71 commando bought in 72, i was thinking about adding indicators but looking at the wiring diagram im a little confused about how the warning light works and gets its earth, it looks like it is connected between the left and right live feeds to indicators, surely that will connect all four indicators at once and still does not explain the earth.
    The rest of the wiring all seems pretty obvious, im assuming the fasher unit is a two pin unit and does it have to be of a certain value.
    Many thanks

    • Hi Bernie – great to hear from you!

      Yes, you are right, the indicator warning lamp looks weird in how it is wired – but that’s the way it was done back in the day.
      – if you turn on the left turn signal, the earth for the warning lamp is achieved via the right front and right rear turn signal lamps.
      – if you turn on the right turn signal, the earth for the warning lamp is achieved via the left front and left rear turn signal lamps.

      Because the wattage of the warning lamp is so low (¼ watt) compared to the two turn signals that it’s pulling the earth through (21 watt each) it is enough to make the warning lamp glow brightly, but the turn signals not glow at all.

      It is important on our old bikes to run the correct wattage bulbs, otherwise you may experience the turn signals flashing at different speeds, or all four turn signals flashing independent of whether you are signalling left or right.

      These flasher units are still available from the usual suspects, including our friends at Andover Norton:

      However, if you are considering LEDs or anything different from the usual, you may want to think about using a more modern flasher unit instead.
      Something like this works well, as they have a positive earth version available:
      These will also allow you to fit incandescent lamps now, and swap to LEDs in the future if you decide to.

      One thing worth remembering with the Lucas turn signals – these get their positive feed from the ‘stalk’ of the indicator.
      These are made of chromed plastic, so the quality of the connection here is the first suspect if you have any issues at all with your turn signals!

      Reach out if you have any further questions, and I’ll do whatever I can to help!


  7. Hi Grant,
    Thanks for posting these diagrams. I’ve been trying to sort the rats nest of wires under the tank from a previous owners attempt at fitting a Boyer ignition. The old black and white diagram I had was not much help!
    The colour coding for the coils, not even marked on my diagram, helped make sense of it all.
    Interesting that I seem to have a Mk3 loom fitted to my Mk2a, it has the WR and WP wires for the starter solenoid but obviously nothing for them to connect to. It may have been fitted by a previous owner but as the bike is original and low mileage I’m wondering if the later Mk2a’s had these looms from the factory?
    Thanks again for saving me much time and head scratching.

    • Hey Mark – great to hear my efforts are helping someone!

      I have certainly not seen a MK3 harness on a MK2a to date.

      In fact, if anything it kinda works the other way – in the first couple of thousand MK3s they used a weird harness which was an evolution of the old one (it even retained the old 3AW silver can assimilator)
      One major difference was that it had an additional three fuses inline which were all hidden away in the headlight bucket – this is often a source of confusion!


  8. Hi I have a 1970 Commando but the kill button doesn’t work but looking at the diagrams can’t see how to get going can you help thanks Dave

    • Hi Dave,

      The 1970 was the first year that Norton moved away from the Wipac Triconsul switch, and across to the aluminium Lucas units that were integrated into the lever perches.

      Do you have electronic ignition?
      Is it fed from the WY (white/yellow) wire that comes from the handlebar switch.
      This wire goes ‘hot’ when you turn on the ignition switch, and should go dead when you press the button.

      Out of the four push switches on the handlebars, this one is unique compared to the other three, as it is the only one that is push-to-break.
      The other three are push to make.

      So this would be the first area to check!
      If the ignition is wired in correctly to this White/Yellow and it is permanently life, even when the button is pressed, it could well be the case that the switch needs rebuilding.

      It is a little fiddly, but take your time – after fifty years, the contacts become corroded.
      I clean them with a fibreglass pencil and some wire wool, and they are usually good to go again!

  9. Hi Grant,

    Thanks for making wiring information available.

    I’ve been rehabbing a 1973 Norton Commando 850 with my Uncle. I’m curious if I can add some notes and clear up some confusion when I was wiring the bike. It would have helped during this project.


  10. Grant,
    I’m working on a MK3 Canadian and having issues with the starter. Installed a new solenoid and when I press the starter bottom I get 1.57v on terminal red/white connected to S terminal on the solenoid. No noise when bottom is press in. I bypassed the solenoid and the starter spins. When I removed the solenoid, I checked for continuity and I do get a beep from the S terminal to ground. From I terminal to ground no continuity. When checking S to I terminal I get nothing. I got this new solenoid from Andover Norton and they are saying I should have 12V on the red/white wire going to the S connection on the solenoid before I press the starter switch. I this correct? I’ve been looking at your great diagram and still scratching my head.

    • Hi Gary,

      There are two smaller terminals on the original starter solenoid.
      One is marked “S” which is for switch – it is the WR (white/red) from the handlebar switch.
      The second terminal is marked “I” which is ignition – it is the WP (white/purple) that goes to the ballast resistor between the coils.
      If you are using electronic ignition, there is not need to connect the WP, as the ballast resistor and condensers are removed.
      It is essential that you have a decent positive feed to the metal mounting bracket on the solenoid – without this, the switch won’t operate at all.

      There should be the full voltage of the battery at the “S” terminal when you press the starter button.
      There should be zero voltage at this terminal at all other times.

  11. On your well appointed MKIII starter rotation diagram you show the starter spinning Clockwise. I have read reliable accounts by world class Norton mechanics that claim the starter spins the other way. Upon bench testing, my starter spins counterclockwise. I saw a video of these very skilled Canadian Norton builders put juice to a rebuilt starter, and it spun counterclockwise. What is the 411.I am baffled.

    • Hi Chris, and thanks for reaching out!

      I have stripped our own MK3 a few times (including converting it to four brush/four coil using the Harley unit for donor parts).
      I can confirm unequivocally that the starter motor rotates clockwise.

      …and in honesty, I am not sure what other detail I can add to my article to prove it (note also in the excerpt from the Norton Factory Worksop Manual at the bottom of the article in the very last pic, it references in the top right “PRESTOLITE STARTER MOTOR (CLOCKWISE ROTATION ON DRIVING HEAD)

      My content is often disputed by “world class Norton mechanics” and I frequently get hate mail from “experts” telling me I’m wrong, I am an idiot, and ‘nothing more than an enthusiastic hobbyist’

      That’s fine by me, as I know my advice is correct, and it’s up to the reader if they take it or leave it.

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