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[duffers]

I am sorry if this question has been asked before I have a 1962 RE 250 crusader which I would like to change from 6volt to 12volt system also at the same time I would like to change it from positive to negative earth.
I just need a simple idiots guide if somebody could help me as I am sure somebody must have done this before me.
thank you in advance for your time

[Adrian]

The 1967 BSA Army B40 wiring diagram can be adapted to suit your switch gear probably more easily than any other bike's system. I would put the original 6V loom to one side and rewire from scratch. You can simplify things by using a combined regulator/rectifier unit instead of a separate rectifier and zener diode. These are also available with built in capacitors in some cases (think Boyer PowerBox or Sparx SPX023) which let you run the bike without a battery if your alternator is in good shape. The reg/rectifier unit will need to be exposed to the airflow for cooling, don't be tempted to mount it inside the toolbox.



If your alternator stator has 3 wires, two of these have to be joined together for 12V so that the alternator is permanently wired for maximum output, I can't remember which just now!



To find a diagram look here and scroll down a bit.



http://bsawdb40.com/Technical-Information



On this sort of bike 12V wiring will be simpler than 6V, you can use 7 core trailer flex (ideally the heavier duty stuff with the grey outer sheath) as the basis for your wiring loom.



A.

[Adrian]

Aggh, forgot! The WDB40 diagram is of course a positive earth system as was standard then, but go carefully and you can adapt it for negative earth. A.

[duffers]

Adrian.
Thank you for that I will have a look at the BSA B40 wiring diagram and see if I can work it out.
Thanks again Dave

[Paulk]

Duffers, If I were doing this I would use a rec/reg as Adrian says. So Alt to reg/rec then to battery just match up red and black to +ve & -ve. (charging done). Cable from preferred earth to frame. Cable from battery (opposite to preferred earth) to ign switch. Then everything controlled by ign switch after the ign switch and everything not controlled before. You can get fancy with relays etc but in essence it all follows the above. If you have an ammeter in the mix, anything that uses short term spikes (horn, brake light etc go before the ammeter as to not send the needle bashing back and forth). This is close http://www.bsabantamclub.com/forum/d10- ... on-a-d144/ If you wish to eliminate bad earths through the frame you can run additional earths to the battery from such areas as tail light assembly, headlight shell and engine - then you don't have to rely on fixings and head bearings to carry a current.

[Adrian]

There was this quite helpful comment posted on the US forum: "I've learned everything I know about it by treating the wires like water pipes."



Extra earth wires are an excellent idea as Paulk points out. You could run one the whole length of the bike from the headlight area (via whatever terminal on the battery you are using for earth) to the tail light mounting studs.



A.

[Gwilly]

Agree with Paul, re the horn but its useful to have the brake light after the ammeter as the deflection shows at a glance that the light is working when braking downhill.

Not easy in daylight to check on the move especially if you have a rear carrier..

Most shorts and poor connections occur on the light wiring especially the rear with its exposed harness, so i think all lighting monitored by the ammeter is useful.

Just saying is all..

[Paulk]

Good point GW. Once you have an understanding that all the circuits are in fact circles (would you believe) ie battery - cable - switch - cable - bulb/coil/whatever - cable (maybe) - earth - battery (think of the kids experiment with a battery, bulb and two wires) you can customize it as you please.

[duffers]

Hi To you all that have helped just like to say thank you for your advice and the time you have taken to help
I think I can work it out now but if I get any problems I will ask again
once again a big thanks Dave

[Coby]

10 Years ago I converted my 1957 Crusaders electrics from 6 to 12 Volts, positive Earth.
This implied a change of all lamps (front and rear now LED), the battery (now 12V 7A gel), coil and regulator (now powerbox by beckelektronika.nl who is the electronics geek for classic bikes in the Netherlands - try Google translate his Dutch site or email him in English). On this Google album you can view pictures and the changed diagram: https://goo.gl/photos/tWyUZTRxRUsrN9iD8

The wiring for the change from 6V to 12V can be left largely intact. By combining the two wires of the alternator coils, and the installation of 2 new wires between the alternator and the new rectifier/regulator it can be quickly arranged. Some other wires are simply disconnected and are not used anymore. There is no need to switch the alternator coils through the lights switch anymore. All three alternator coils are used continuously and the voltage regulator ensures that the battery level keeps tidy. The 'emergency' start is not needed. The system is reliable enough to do without.

For my Crusader it's a success.
Hilbert