Norton Commando Wiring Diagram + Boyer

Grant Tiller

A really popular Norton Commando upgrade is to move from the old points-based ignition system over to Electronic Ignition.

One of the most common units of the time is Boyer Bransden, who have been around since 1969.

Grant Tiller

They are still going today, and their website can be found here.

Moving from points to Boyer electronic ignition is a pretty simple upgrade.

From a wiring perspective, the most important thing to note is that you will be moving from a pair of coils that are wired in parallel to series.

Originally, the points make and break the positive (earth) side of each coil in turn.

The Boyer electronic ignition system uses a concept called “wasted spark” – with the two coils wired in series, they are energized together on every rotation of the camshaft.

You’ll note in the wiring diagrams below that the Ballast Resistor and Condensers have been removed as part of the conversion to Electronic Ignition.

The color coding of the wiring is simple:

  • The Red – this is the positive feed to the Boyer, and is usually picked up from the red wire that goes to the Coil positive terminal.
  • The Black – this is the negative supply FROM the Boyer TO the coils.
  • The White – this is the negative feed to the Boyer. This joins in to the White/Blue wire that used to feed the Ballast Resistor that you are removing. As standard, this goes up to the big connector block under the tank, where it’s joined to the White/Yellow that is the kill switch on your left side handlebar switch cluster.
  • Black/Yellow and Black/White – these go from the Boyer black box (they call it the Transistor Box) down to the Stator Plate that sits behind the points cover.

Here is the factory wiring diagram with the Boyer unit added into the circuit.

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

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

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

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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

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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

Note – the wiring is the same for both the Boyer Bransden Micro MKIII and Micro MKIV systems.

NOTE:

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!

2 replies

  1. Hi, could you please tell me if you have in stock a coloured wiring diagram for a Mk11A Norton Commando, with a Boyer Mk111 unit, type Norton Mk111, fitted with a power box, single phase input alternator 180watts, output 12volt dc, 13 – 14.5 volts, 15amps. If so, I would like to purchase one.

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