Norton Commando Wiring Diagram + Tri-Spark

Grant Tiller

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 point 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.
  • 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. circuity 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)

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

Grant Tiller

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

Grant Tiller

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

Grant Tiller

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

Grant Tiller

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

In the very early days of Tri-Spark, a few people reported Early Life Failures – i think due to over heating.

However, there have been a few minor revisions along the way, and these units are now proving to be superbly reliable.

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. just what i needed last year when i renewed my loom . i have a trispark ignition and alton starter so this would have been perfect, as i lent my wiring diagram and clymer manual and never got it back .so i will save your brilliant diagram and thanks for putting this on the norton owners club, and keep up the good work cheers neil

    • Thanks so much Neil!
      …sorry I didn’t get to you sooner!
      Print it out and stick it on your wall, they blow up to A3 quite well, and would be nice laminated!

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