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May 20, 2020

Custom Norton 1972 Commando Wiring Diagram – Benji Bishop

by Grant Tiller
Grant Tiller

Benji has a 1972 Norton Commando.

This bike has all the superfluous Interpol wiring removed.

Also, it has no Power Socket.

 

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.

 

Another 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.

The most common manufacturer of these is Podtronics.

Grant Tiller

There are four wires to connect:

  • Two Yellows – these are the AC input 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)
  • The Red – this 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)
  • The Black – this 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)

 

A worthwhile upgrade that is worth it’s weight in gold is adding a Charge Warning Light in lieu of the standard warning light assimilator.

Grant Tiller

The nice thing about the Improving Classic Motorcycles unit is that you can retain the original warning light – so it looks totally factory.

It gives you a lot more useful information about the state of the battery and charging system compared to the standard assimilator unit, which looks for AC output from the alternator stator only.

Grant Tiller

 

 

Here is the wiring diagram with the Interpol wiring removed, a charge warning light and Boyer Bransden Electronic Ignition and Podtronics regulator/rectifier added:

Custom Norton 1972 Commando Wiring Diagram – Benji Bishop PNG 3066×1841
Grant Tiller
But wait…
Benji mentioned that he was planning on buying the wire and making a wiring loom himself.
That kind of got me thinking about what I would do if i was starting from scratch and using the same components that he’s got.
First off, i’d get rid of as many connectors as possible, especially the big one under the fuel tank – there is simply no need to have it there.
Next I would sort out the earthing/grounding which is notoriously poor on these bikes.
So here it is – my version, and what I would do:
Alternative Custom Norton 1972 Commando Wiring Diagram – Benji Bishop
Grant Tiller

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