Custom Norton Commando Wiring Diagram – Negative Earth (Rick Peebles)

Rick Peebles reached out through the Norton Commando Facebook group for a hand rewiring his bike.

Grant Tiller

Rick has got quite a few non-standard parts on his bike, some helping out on this one was quite interesting.

In addition, Rick has gone negative earth on this bike too – so a bit of a challenge.

Grant Tiller

Electronic Ignition

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

Tri-Spark get a bad press for reasons I have gone into in an article here – I have never, ever had an issue with them – always reliable, great customer service, and full of some great features.

They are my personal preference for electronic ignitions, and I recommend them to anyone thinking of moving based on my own great experience.

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.

For negative earth as on Rick’s bike, the wiring is as follows:

  • Red wire – this is the positive feed to the Tri-Spark unit. This attached to the coil positive and marries up to the WU (white/blue) that comes from the kill switch on the handlebars
  • Black/Yellow – this is the negative feed to the Tri-Spark unit. Rather than earth this on the timing cover mounting post, I much prefer to run a separate wire up to the engine earth up at the head steady – it is much, much better.
  • Black/White – this is the negative supply FROM the Tri-Spark TO the coil negative terminal.

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.

With a single coil as Rick has gone for, both spark plugs are ignited via the one coil instead.

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)


In lieu of the twin 6 volt coils, Rick has gone with the dual output single tower coil which looks much neater.

Grant Tiller

One point worthy of note with dual output single tower coil conversions is sparkplug choice.

Most people don’t realise that with this type of coil, the sparks at the sparkplugs jump the opposite way on one lead.

So for one sparkplug, the spark jumps from the centre electrode to the ground electrode (as you’d normally expect)

However, for the other sparkplug, the spark jumps from the ground electrode to the centre electrode (which is opposite to what you’d think)

Therefore, when choosing your sparkplugs, you need to bear this factor in mind!

Many people go for precious metal plugs – like platinum or iridium.

The benefit of these plugs is longevity – they simply last longer.

With the spark jumping from the ground electrode to the centre electrode, this benefit is totally lost.

The answer is to run double platinum or similar plugs, where a precious metal is used at BOTH the centre electrode AND the ground electrode.

My personal preference is the Denso VW22 plug – this has a platinum pad on the ground electrode and an iridium centre electrode.

I like Densos as they just seem to last forever – I use the IW22 on twin coil bikes, and their VW22 is the ‘twin precious metal’ equivalent.


Rick has fitted a 3 phase Lucas alternator – a nice choice for superior charging in modern traffic conditions, since the same output is achieved at a much lower RPM

Grant Tiller


Another of the most common upgrades or modifications for a classic british bike is to add a combined regulator/rectifier unit.

Our Commandos use a blue can capacitor, zener diode (which can be found mounted on the back of the z-plate) and rectifier unit.

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

The most common manufacturer of these is Podtronics and Rick has gone for the three phase version to match his new stator.

Grant Tiller

There are five wires to connect:

  • Three Yellows – these are the AC input and pick up on the three wires that come from the alternator stator. The connection can be any way round, as this is the AC side of the circuit, so polarity is not important.
  • The Red – this is the Positive output and will join to the positive battery terminal via it’s own dedicated fuse.
  • The Black – this is the Negative output which goes to the battery negative terminal.

Switch Gear

Rick has dropped the standard Lucas aluminium switchgear – this is sometimes a necessity when you upgrade your levers (upgraded brake master cylinder, and a hydraulic clutch in this case.)

So he has gone for a Universal handlebar switch on the left side from K&S technologies.

This “Honda Style” switch takes care of lights dipped/main beam, left and right turn signals and horn – and is mounted on the left side.

The markings on the packaging are: XR-650L Type K&S No 12-0046

Confusingly, there seem to be different versions of this switch available with the same K&S part number.

Rick’s is the one with the gray turn signal switch, and the two extra wires.

Grant Tiller

The wire color scheme makes this a little confusing when it is inserted into the wiring diagram, as obviously it does not confirm to the classic British color code.

Grant Tiller

On the right side, is just a simple two wire engine kill switch.

Grant Tiller

Turn Signals

Rick has gone for X-Arc Signals from HighTechSpeed

You can read more about these amazing ultra bright LED turn signals here.

Grant Tiller

These are made of billet aluminium, and can be programmed by using a magnet on the casing to enter programming mode – very clever.

They have four wires:

  • Black => Negative
  • Red => Positive Running Light
  • Orange => Positive Brake Light
  • Yellow => Positive Turn Signal
Grant Tiller

Rick is using them as turn signals only on the front, so will use the black and yellow wires.

On the rear of the bike he is using the brake light functionality too, so will tap the orange wires on the X-Arc units into the brown wire that goes to the brake light.


In order to use LED turn signals, it is important to change the factory standard Lucas flasher module – becuase it requires two 21 watt incandescent lamps as load in order for them to work properly.

Rick has got an LED compatible flasher unit.

12V LED compatible flasher unit CF12 (2 pin)

Grant Tiller

For negative earth bikes like Rick’s, it is wired as follows:

  • Terminal marked “L” => wired to the handlebar switch
  • Terminal marked “B” => wired to Pin 2 of the ignition key switch (the hot live)

It is worth noting that positive earth bikes are wired the opposite way round.

To retain the Turn Signal Warning lamp and have it driven from a 2 pin flasher relay, it is necessary to install a “tweaker” on the lamp. This is a simply a pair of diodes installed on the positive feed side of the warning lamp.

Tidy Up

Rick has taken the opportunity to remove the superfluous Interpol wiring, as of course it is not required.

In addition, he has also removed the Power Socket too.

The final thing to note is that Rick has added one of Donald Pender’s superb oil pressures switches – a very useful addition!

Wiring Diagram

Here is the wiring diagram for Rick’s Commando.

Rick Peebles Custom Norton Commando Wiring Diagram – Negative Earth PNG 3066×1841

This is available as a PDF too – it can be downloaded here.

Grant Tiller

Leave a Reply

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