Greg Marsh Enterprises – Custom Wiring Diagram

Grant Tiller

Greg Marsh from the Access Norton forum reached out to ask for some assistance with a wiring diagram.

Greg has already modified the original Bill Turnbull diagram (which you can find right here to accommodate some of the changes he has made. However, I have since made several changes and edits to Bill’s original (as well as covering the older models)

Greg has actually done all the work already, designed and built a superb, bespoke wiring loom.

He has documented it all in great detail over on his website, which you can find here.

The purpose of building a Wiring Diagram after the event is to help others that want to follow Greg’s superb example!


Greg has done the usual thing and swapped in a modern regulator/rectifier in lieu of zener diode and lucas rectifier (Greg has chosen to retain the capacitor).

Our Commandos use a lucas full wave rectifier and separate zener diode (which can be found mounted on the back of the z-plate) and rectifier unit.

A combined regulator/rectifier replaces both of these components with one package.

Greg has gone for the new to market Tri-Spark MOSFET unit.

Grant Tiller

It is certainly easy to spot in it’s blue anodised heat sink!

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)

The spec on paper is very good, being able to handle up to 20 amps.

And the benefit of MOSFET is much more precise control of the charge voltage.

Here are the wiring instructions for the Tri-Spark VR-0030 MOSFET regulator/rectifier.

Grant Tiller

Electronic Ignition

In addition, he has chosen to go up the electronic ignition route in lieu of points, condenser pack and ballast resistor.

His choice is the excellent Tri-Spark Classic Twin.

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.
  • 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)

Simplified Wiring

However, it is some of the other upgrades and optimisations here that Greg has made in order to give simplicity and reliability that has really piqued my interest!

For example, he has removed the main connector block found under the fuel tank – a popular home for many faults and unreliability.

Wherever possible Greg has removed the bullet connectors, choosing to wire from the connector of the component itself straight in to the wiring loom.

He has run a 14 gauge red wire from front to back, splicing in to it wherever a component needs a ground. This negates the unreliability of using the frame as a ground, and relying on painted/rusted surfaces for electrical conductivity.

All of his joints are soldered and heat shrinked, and i am very impressed with the quality of his work.

It’s well worth popping over to his website to see how he’s done it!

Wiring Diagram

So without further ado, here is the Wiring Diagram!

Greg Marsh Enterprises – Custom Wiring Diagram PNG 3066×1841

Grant Tiller

Greg says on his website “It might sound strange, but I like wiring Vintage British Motorcycles!”

It might sound really, really strange, but I really enjoyed helping out by putting this wiring diagram together!

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