Custom Norton 1972 Commando Wiring Diagram – Vaughan Rochford

Grant Tiller

Vaughan has a 1972 Norton Commando.

It’s got a new loom which is correct for the bike.

However, Vaughan  has the older headlamp shell which incorporates the Ammeter as seen on the pre-1971 models.

Grant Tiller

When you are doing this conversion, it is important to run two wires to the headlamp shell that can take the ENTIRE current of the bike.

A minimum specification of 2.0mm², 25.0A cable should be used.

My personal recommendation would be to go up a size to 3.0mm², 33.0A cable instead.

It is important to put the Ammeter in this specific location, so you can see it swing both ways (ie a charge from the Alternator when you are running at speed, a slight discharge at engine idle)

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 wiring diagram with the Boyer unit and Ammeter added into the circuit for Vaughan’s bike.

Custom Norton 1972 Commando Wiring Diagram – Vaughan Rochford PNG 3066×1841

Grant Tiller

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