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.

The new kid on the block for Electronic Ignitions is Tri-Spark.

Well, I say new kid – they have been around since about 2009.

You can find the Tri-Spark website here.

Grant Tiller

The Tri-Spark unit is a one box solution – all the gubbins are mounted inside the points cover – no additional black box to try and hide under the tank, and very very simple to connect up.

The wiring is as follows:

  • Red wire – this is the positive feed to the Tri-Spark unit. Most people attach this wire to one of the two fixing posts inside the points cover. I would personally recommend running an additional wire up to the coils.
  • Black/Yellow – this is the negative feed to the Tri-Spark unit. 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/White – this is the negative supply FROM the Tri-Spark TO the coils.

As with the Boyer, 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 Tri-Spark 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.

Two major benefits of the Tri-Spark:

  1. a very low operating voltage – as low as 8 volts means your bike will still run with a less than optimal battery and charging system
  2. circuitry performs the electronic equivalent of advance and retard to make the bike easier to start and stop the possibility of kick-back. This makes it gentler on your knees, and kinder to electric start systems (aka the delicate Commando sprag clutch)

Here is the wiring diagram with the Tri-Spark unit and Ammeter added into the circuit for Vaughan’s bike.

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

Grant Tiller

3 replies

  1. Mark can you help me,
    I have a 1971 Norton commando and has a Boyer Bransden Mark 3 electronic ignition system already fitted, so I wanted to fit a Boyer Bransden Power Box as I am rewiring the bike.
    I have purchased the box model number 00166 12V with charging light, but I have been told that power box could be effected by the warning light assimilator, and because of this the assimilator should be removed when the power box is used.
    The power box 6 wires, two Yellow from alternator , one Black negative.one Red positive, one White and one Red/White to connect to charging lamp.
    Do you have a drawing showing how it should be interfaced with the Norton wiring diagram?
    I think one of your drawing (the 1971 three wires to the master switch) is closet to my bike wiring.
    Thank you for your help
    Regards
    Mike Warner

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