Norton Commando Wiring Diagram with Boyer electronic ignition and reg/rec

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.

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Boyer Bransden 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:

Wire ColourDescription
Redthis is the positive feed to the Boyer, and is usually picked up from the red wire that goes to the Coil positive terminal
Blackthis is the negative supply FROM the Boyer TO the coils
Whitethis is the negative feed to the Boyer – it 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. If the white/yellow is long enough, you can connect the white wire of the Boyer directly to it!
Black/Yellow and Black/Whitethese go from the Boyer black box (they call it the Transistor Box) down to the Stator Plate that sits behind the points cover.

The Boyer Bransden Micro MKIV is the current iteration of their Electronic Ignition system, and offers a few improvements over the MKIII – including a slightly optimized timing curve which improves stability at engine start, plus the ability for the electronics to run at lower voltages (10 volts)

The old Boyer MKIII liked a good, strong 12 volts, and this was the cause of backfiring, particiuarly on the Electric Start Commando MK3

The Instructions specific to the Norton Commando that come with the Boyer Bransden Micro MarkIV can be found here:

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Here is the Boyer Bransden Micro MKIII General Information Sheet

Here is the Boyer Bransden Micro MKIV General Information Sheet


One of the most common upgrades or modifications for a classic british bike is to add a combined regulator/rectifier unit.

Our Commandos use a blue can capacitor, zener diode (which can be found mounted on the back of the z-plate) and rectifier unit.

A combined regulator/rectifier replaces all of these components with one package.

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Boyer Bransden are also popular manufacturer of aftermarket regulator/rectifiers with their Power Box units which are available in single phase, three phase and high power versions.

Bike owners that have gone up the route of Boyer electronic ignition often choose to install the Boyer reg/rec too, as many like them to match.

However, one very important thing to note, which often gets overlooked is that the Boyer Bransden Power Box is not compatible with the Warning Light Assimilator used on the Norton Commando.

You can see in the note below:

If your Norton has a charging warning light simulator it must not be used with the
power box, remove it. If the light control is required fit the power box type
PBOX00166 with charging light control.

While the wording is poorly put, and the grammar is bad, the message is very clear.

You can see the original instructions here:

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As you can see in the instructions, Boyer Bransden sell a different Power-Box unit, if you want to continue and use the red warning light to show charge. It is the PBOX00166 model.

The Instructions that come with the PBOX00166 Boyer Bransden Power_box regulator/rectifier with charging light control can be found here:

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There are six wires to connect:

Wire ColourDescription
Yellow (x 2)these are the AC inputs and pick up on the Green/Yellow and Green/White (connection can be any way round, as this is the AC side of the circuit)
Redthis is the Positive output and will join to the red wire if you are using existing wiring (it goes straight to the ground/earth of the frame)
Blackthis is the Negative output (known as the hot wire) – it will pick up on the Brown/Blue wire (which goes via a fuse straight to the battery negative terminal)
Whitethis is the positive feed to the warning lamp – it is switched by the reg/rec based on the presence of an AC output from the stator
Red/Whitethis is linked in to the Red ground lead

Wiring Diagrams

Here are the factory wiring diagrams with BOTH the Boyer Electronic Ignition and Regulator/Rectifier units 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 (l fuses in the headlamp shellPNG 3066×1841

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1975 MK3 (Original) PNG 3066×1841

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1975 MK3 (Canadian Market) PNG 3066×1841

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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!

This article is from a series of three covering Boyer Bransden products:

As always don’t hesitate to reach out if you need any help or advice.

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