Phil Baker has a MK3 Norton Commando that he is in the process of fitting LED warning lamps to.

This is no problem at all – the only thing to watch out for is the polarity – an LED cannot be connected either way round like a filament lamp can.

Turn Signal

There is one minor complication though – and that is with the turn signal warning lamp.

A two wire Lucas flasher unit is fitted to the bike as standard.

This consists of a bi-metallic strip, as it gets hot (from driving two 21 watt filament lamps) the strip breaks contact until it cools again at which point the circuit is re-made. This is the action that makes the lights flash.

The warning light in this setup is driven through the turn signal lamps, and interestingly when the left lights are flashing, it is the right side that is providing the positive supply (earth) to the warning lamp.

In the same manner, if the right lights are flashing, it is the left side that is providing the positive supply (earth) to the warning lamp.

Of course, the second you fit LEDs (either in lieu of the 21 watt turn signals themselves or as the warning lamp) this methodology no longer works anymore.

That is because, with an LED (light emitting diode) current is only able to flow in one direction.

All is not lost though – there are two fairly simple ways you can get things going!

Tweak

The first way is to use a tweaker

A tweaker is nothing more than two diodes soldered to some flyleads and made robust by packaging it in heatshrink tubing.

They are available in a number of different places, or alternatively you can easily make your own.

If you buy one, it is essential that you make the seller aware that your bike is positive earth.

A good UK source of tweakers is UK community bike electrics guy Paul Goff

Here is a link to the tweakers on his website.

Here is a wiring diagram showing LED warning lamps, and a tweaker in place for the Turn Signal Warning lamp

Custom Norton Commando Wiring Diagram – Phil Baker PNG 3066×1841

This is also available for download as a PDF

Flasher

The other alternative (and my personal preference) is to fit a modern flasher unit instead.

These are solid state (no more bimetallic strips), have a separate feed for the warning lamp, and also means that you can fit LED turn signals in the future if you want, without having to worry about adding extra load resistors to stop the flashing too slowly, or worse still staying on all the time.

There are several options available, but I recommend Classic Car LEDs as one worthy of consideration.

They have a solid state unit available, and the option of Positive Earth – so perfect for our bikes.

The reason I like these units is that the same unit will support incandescent lamps or LEDs, so there is a good degree of future proofing.

The unit is a simple canister design, and can easily be hidden away on the bike.

Here follows a copy of the wiring diagram as per their website:

You will note that this has a separate line to the warning lamp, which means no requirement for additional diodes (tweaker).

Here is a wiring diagram showing LED warning lamps, and a modern flasher unit in place to drive the Turn Signal Warning lamp separate to the turn signals.

Custom Norton Commando Wiring Diagram (alternative) – Phil Baker PNG 3066×1841

This is also available for download as a PDF