Norton Commando Wiring Diagram + Boyer + Sparx 3 phase

Grant Tiller

“dguzzi” from the Access Norton forum reached out and asked for a diagram that incorporated the Sparx 3 phase alternator and combined regulator/rectifier.

Sparx was setup by Andy Gregory – the Triumph Parts Specialist – AKA Tricor Andy

Personally, I am not a big fan of Andy, or Sparx – having received very poor customer service from him in the past when trying to fix someone’s Triumph Bonneville wiring issues.

Sparx are also known for their aftermarket handlebar switches too.

Grant Tiller

I fitted a Sparx 3 phase high output alternator to a 1965 Triumph Bonneville T120 and wasn’t overly impressed.

The hole through the rotor was too small to fit over the crankshaft.

When questioned, I was told this was by design and that it should be broached on to the crankshaft by ‘whacking it on with a mallet’ then ‘graunching up’ the retaining nut.

That’s all well and good, but what about the poor guy that needs to get it off in the future?

Instead I used a reamer and reamed the hole out to fit. It was a nice snug fit, just like the Lucas rotors are right out of the box!

Grant Tiller

The rest of the alternator kit was OK.

The regulator/rectifier AC wires were all yellow and the alternator stator wires were green and white, which was a bit weird considering it was supposed to be one kit from one manufacturer – I was surprised they didn’t make an effort to standardise on wire colours.

Not a major issue though, and me just being a bit ‘nit picky’

One thing that did surprise me was the Instructions:

Grant Tiller

I was surprised that the instructions referred to using 5K resisted spark plug caps at the top of the page and stating that failure to do so will cause overloading.

Then at the bottom of the page it refers to using resisted spark plugs, as circuitry is sensitive and failure to do so will cause over charging.

These are the kind of disclaimers I would expect to see in the documentation of electronic ignitions, where there is a conversion of analogue rotation to a digital trigger signal, which can indeed be susceptible to radio frequency interference (RFI) or electro-magnetic interference (EMI)

Probably a sign here, I feel, that very poor quality components have been used.

Here is the circuit diagram which incorporates the Sparx3 phase high output alternator kit together with Boyer Bransden electronic ignition:

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


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!

Leave a Reply

Your email address will not be published. Required fields are marked *