Walt (username WEM) from the Access Norton Forum has been having a few issues with charging and melting wires on his 1974 Commando.

Originally, Walt’s wiring would have looked like this:

A few years ago, he added a Podtronics regulator/rectifier, so the wiring is currently looking like this.

(Note that Walt still has the blue can capacitor on his bike):

Walt has recently had some issues with fuses blowing and fuse holders melting.

We have talked him through some tests for the Warning Light Assimilator, Alternator Stator and Reg/Rec and we are seeing some varied results.

Alternator

During the course of this winter, Walt is considering replacing his single phase alternator stator with a three phase one.

The three phase Lucas alternator is a nice choice for superior charging in modern traffic conditions, as you will get a decent output much power down the rev range.

Regulator/Rectifier

I have also recommended that Walt considers fitting the superb Shindengen SH775 regulator/rectifier – it will handle his new three phase alternator stator, plus it is a much smarter choice than the legacy Podtronics.

This unit’s wiring is identical to the Podtronics it would be replacing, which in turn is a direct replacement for the original Lucas rectifier.

However, I suggest, based on issues experienced up to this point, that Walt considers making a few minor changes as detailed on this page.

The Shindengen is wired in the same way as most aftermarket reg/rec units:

I am not sure how Walt wired the Podtronics originally, however, when it comes to the Shindengen reg/rec and the new 3 phase alternator stator, I would be inclined to run new wires rather than reuse the original ones in the harness.

The reg/rec is wired direct to the battery via it’s own dedicated fuse (as I will come on to next) so there is no need to try and reuse the original R (red) and NU (brown blue) wires that went to the rectifier originally.

The same is true for the two wires GY (green yellow) and WG (white green) that go to the alternator stator. You are moving to a three phase stator, so need an extra wire anyway – so it just makes perfect sense to run three new yellow wires from the reg/rec directly to the alternator stator instead of trying to reuse the original wires (which we know have given you trouble in the past anyway)

Just make sure that you securely tape up these wires (ideally use some heatshrink tubing) to ensure they are protected and do not come into contact with anything accidentally. Where the wires loop in and out, make sure that loop is maintained so that everything further down the chain (for example the ignition switch that feeds switch power to the rest of the bike) stays connected and working!

Fuses

Considering the previous issues of fuses blowing and wiring/fuse holders melting, I personally feel it is a good idea for Walt to wire his new reg/rec directly to the battery via it’s own dedicated fuse.

I would recommend using automotive blade type fuses for both this, as well as the original one on the bike.

These are great, as blade fuses are available in every garage, and are very resiliant to vibration.

You can use a 15 amp fuse for both.

Charge Warning Light

A worthwhile upgrade is the Charge Warning Light.

The factory warning light assimilator (the Lucas 3AW 3 wire ‘silver can’ assimilator) is very unreliable, and only gives you information that a single phase alternator stator is putting out ‘some’ AC. Not very helpful!

Also, the 3AW can either fail open or fail closed, and can cause major issues with your charging system.

The nice thing about the Improving Classic Motorcycles unit that I recommend here is that you can retain the original warning light – so it looks totally factory.

It gives you a lot more useful information about the state of the battery and charging system compared to the standard assimilator unit, which looks for AC output from the alternator stator only.

The old wires that feed the Lucas 3AW warning light assimilator are no longer needed.

These will be:

• R (red) – positive feed
• GY (green yellow) – the AC feed from one leg of the rectifier (which you have disconnected anyway with the addition of the new Shindengen reg/rec
• WN (white brown) – which heads off to the front of the bike to the lamp in the headlight bucket

While these are now superfluous to your needs, as with the reg/rec and alternator stator before make sure that you tape up (or heatshrink) the unused wires to make sure they do not accidentally short on anything else. Always be sure to maintain the loop of the red if there are two wires going in and out again – it is important to maintain this continuity as it is your positive feed to the rest of the bike. It’s quick and easy to do, and will save you from issues further down the line.

You can easily pwire up your new charge warning light inside the headlight bucket. The wiring is simple:

• R (red) – this will piggyback onto the other side of the lamp holder, which already connects to your positive earth feed
• S (slate) – this will go to the other side of the lamp holder, which was formerly connected to the WN (white brown) that went to the old 3AW warning light assimilator
• B (black) – this will pick up one of the “switched hot” white wires that comes from your ignition switch – there are several of these in the headlight bucket that you can pick up on.

Charging System

Here is a diagram that shows the evolution of the charging system on Walt’s bike.

As he is moving from single phase to three phase, I would suggest that he doesn’t try to reuse the GY (green/yellow) and WG (white/green) wires.

We have had issues with these anyway, plus he is moving to three phase, which will require an extra wire.

Capacitor

I have recommended to Walt that he leaves out the blue can capacitor.

From my own testing, I have found a couple of things:

• The blue can capacitors start to deteriorate significantly after about two years of being on a bike.
• A lot of Podtronics units I have seen over the last couple of years contain a capacitor in them already (ie I am seeing a charge across the red and black leads after the reg/rec has been removed from the alternator stator and the battery)
• The new aftermarket ‘Sparx’ branded capacitors are very unreliable – there was even a batch last year that had the positive and negative terminals labelled incorrectly.
• A good, modern battery does a much better job at smoothing voltage than a capacitor ever could (not the case with the old wet batteries from the 70s)

Of course, there is no issue if you choose to leave the blue can capacitor on your bike.

It’s just my preference to remove them based on my own findings.

So here we go – below you will find a complete wiring diagram for Walt’s bike based on the changes I recommend he implements over the winter.

Custom Norton Commando Wiring Diagram – Walt (WEM) PNG 3066×1841

Updated for 2023

Walt has reached out, as he is in the process of upgrading his ignition to the excellent Tri-Spark electronic ignition.

You can find the Tri-Spark website here.

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 and have drawn the wiring diagrams accordingly.
• 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.
  IF your White/Yellow kill switch wire is long enough, you can bypass the White/Blue and get rid of another connector!
• Black/White – this is the negative supply FROM the Tri-Spark TO the coils.

As with most electronic ignitions, 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 diagram shows that the Ballast Resistor and Condensers have been removed as part of the conversion to Electronic Ignition.

There are 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)

Updated Wiring Diagram

Here is the updated Wiring Diagram for Walt’s bike:

Updated Custom Norton Commando Wiring Diagram – Walt (WEM) PNG 3066×1841

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