Author Topic: basic B40 electrics then to upgrade  (Read 255 times)

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  • Golden Flash
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basic B40 electrics then to upgrade
« on: 13 August, 2021, 17:24:21 »
Ok, I have been playing with wiring for years but this one is baffling me, must be going senile  in old age.

its a 1965 B40 only has the Green/White and green/yellow wires from the generator so a 6V system.
its got side points and a coil and kill button. just cant get a spark (wired by my son !!)

all wiring diagrams Ive seen have three wire generators or are original with switches and rectifiers fitted.

what Im looking to do is a basic wiring diagram  to get the new built motor running. do I need rectifier
as the bike is going to be a day use only, at the moment, I would then be looking at adding rear brake light and horn.
the option to add ignition switch , battery and head and tail lights.

the question arises, whats the best , to convert to neg earth or leave pos?
also is 6v good enough or go 12v?

obviously, the last two questions will or should impact on the diagrams for the first questions.
thing is , Ive already got a lot of money into the rebuild and dont want to spend out on a lot of fancy electronic bits and pieces , if it ends up not needing the extras.
currently have the T100 and A10 sat in garages that have not moved in 4or 5 years.


  • Empire Star
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Re: basic B40 electrics then to upgrade
« Reply #1 on: 13 August, 2021, 18:09:58 »
Two wire alternators are for 12 volt.

One wire white with green tracer (WG) the other Green with yellow tracer. Coils set in resin.

Below a basic wiring diagram from the 1971 Lucas Service manual. Battery optional.

The 2MC capacitor is quite a large item but I suspect that there is a more recent solid state item to replace the rectifier/2MC capacitor/zener diode.


  • Golden Flash
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Re: basic B40 electrics then to upgrade
« Reply #2 on: 13 August, 2021, 19:33:20 »
thanks Julian
Ive only ever encountered 3 wire generators in the past.
Im forgetting more things every time I look at the bikes... :'(


  • Royal Star
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Re: basic B40 electrics then to upgrade
« Reply #3 on: 16 August, 2021, 09:35:44 »
The 3 wire alternator has to be connected to the light switch so that it gives more power with lights on. A simple solution for not overcharging the battery. It can be used with a modern rectifier/regulator with (the right) two leads connected together. The later 2 wire alternator was to be used with a Zener diode preventing overcharging of the battery.
I suggest you check on Paul Goffs website Lots of useful information there
I've bought parts from him for a complete rewiring of my WD B40.