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8 Easy Steps to Fit Modern Electrics onto a Classic Bike

You've bought an old British bike and you're going to restore it or turn it into a custom bike. You know there is a cool ride beneath the rust, peeling paint and puzzling electrical system.


Many old motorbike fans say “I can do the mechanical stuff but not electrics, I just don’t understand it” If you completely renew the electrical system on your old bike then you will soon realise just how simple it really is.


This article deals with the electrics on a typical British motorcycle with kick start and alternator from about 1960 onwards. Triumph, BSA, Norton, whatever, it applies to all.


Warning: If you are aiming for a restoration to factory original specification look away now, this article is not for you. You will replace the ignition system, coil, battery and some bulbs with
modern equivalents. You will also make your own wiring loom to connect all these together.

Step one: battery


Fit an AGM type battery of 7 or 9 Amp hour rating. These are maintenance-free and can be left unused for months. The battery will be smaller than the lead/acid type.
Make a custom size battery tray or pack out the standard tray with a closed cell foam such as Plastazote.

Step two: electronic ignition (EI)

There are many systems out there but I recommend the Wassell system, it is reasonably priced, easy to fit and rugged.


Electronic Ignition kit


<Wassell Electronic Ignition system>

Step three: ignition coil


Modern EI allows you to replace two coils with a single “dual output” coil. Locate it beneath the battery tray. This will free up space under the seat where the coils
used to be. Use this space to mount the Electronic Ignition “black box.”


Dual Output Coil

 <Dual output coil>

Step four: regulator and rectifier


Replace the regulator and rectifier with a modern combined “reg/rec” unit such as made by Podtronics. Mount the reg/rec somewhere ventilated otherwise it may
overheat and fail.


Podtronics Reg-Rec

<Podtronics reg/rec>

Step five: blade type fuse box


Blade fuses are fitted to all modern vehicles and are widely available. The fuse box allows separate circuits e.g. lights, horn, indicators and brake light. Select a fuse box with one common input terminal and four fuses. Wire the battery to it via the ignition switch. Put a 20 amp fuse in this wire. You may find some trial and error necessary but start with these fuses:


Lights: 7.5 Amp

Horn: 7.5 Amp

Indicators: 5 Amp

Brake light: 5 Amp


Step six: LED bulbs


Light Emitting Diode bulbs are very bright, very robust and draw less current than conventional bulbs. An LED stop/tail bulb is available. If you only fit one LED bulb
make it this one. Important: LEDs are usually negative earth. Most old British bikes were positive earth so you may need to change that. If your bike is still positive earth you will have to find positive earth LEDs.


Step seven: dedicated earths


Provide an earth point at the front of the bike and connect switch and headlight earths back to it. Inside the headlamp shell is ideal. Make another earth connection to the top of the motor where it bolts to the head steady. Run an earth wire from these and any other components to a terminal block mounted near the battery. Connect this with one lead
to the battery earth terminal. Now everything is earthed through dedicated wiring and not through the frame.


Step eight: make the wiring loom


Attach the new components to the bike. Sit down with a sheet of paper and draw the components on it. Now “wire” it up on paper using different coloured pens. Doing it this way helps you get the whole concept of how it all connects. Use whatever wiring colours you like but I prefer these:


  • Red Always on From battery to ignition switch
  • White Switched From the ignition switch to ignition and fuse box
  • Green Fuse box to headlight switch
  • Yellow  Headlight switch to main beam and tail light
  • Yellow/Black Headlight switch to dip beam.
  • Brown Fuse box to brake light switch and brake light
  • Blue Fuse box to horn
  • Black All earths

Tips: Use a black marker to add a black trace e.g. make some yellow cable into yellow/black Use new 3.9mm Japanese style bullet connectors to connect everything up
followed by a wrap of self amalgamating tape. Plastic sleeving is useful at stress points e.g. where wiring goes from frame to headlamp.

The care it deserves


Hopefully by now you feel ready to have a go at the electronics on your classic motocycle restoration project. If you're yet to meet your classic motorcycle restoration project, you can find motorcycles for restoration online. When done right, you will get the unbeatable looks of a classic motorcycle combined with the convenience of modern electrics.

When you're almost ready to get your restored classic motorbike on the road, don't forget to take out dedicated classic motorcycle insurance. With great policy benefits, Carole Nash will give it the care it deserves.


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