Norton Commando Wiring Diagram + Power Arc

Grant Tiller

I have fitted a Power Arc electronic ignition to my bike.

Grant Tiller

These are sold, I believe exclusively for Norton Commandos by Fred and Ella at Old Britts.

This is a brilliant company to deal with, polite, efficient and courteous.

What Old Britts don’t know about Norton Commandos isn’t worth knowing!

Grant Tiller

The reason I have gone for the Power Arc kit is two fold:

  • it supports several different ignition curves, which you can tweak yourself on a laptop, then easily switch between on the bike.
    I like the idea of an around town map and a fast road map – and I guess time will tell how practical and/or useful that is!
  • the sensor is optical – most of the common electronic ignitions systems (like the brilliant Tri-Spark, which I have fitted to other bikes) use a spinning magnetic rotor.
    The Power Arc uses a slotted optical disc and encoder arrangement, so in theory should be more accurate, and have better longevity.
    Again, time will tell on that one!

Here follows the wiring diagram for the Power Arc electronic ignition.

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

Grant Tiller

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

Grant Tiller

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

Grant Tiller

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) PNG 3066×1841

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

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

Grant Tiller


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

  1. 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.
  2. 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!

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