CJ750 toolbox
Wiring in a 12V regulator to a 6V generator by John Nash
This is not my own work. Sean Hawker (of Hawker Eectricals) supplied me with the regulator and the wiring guidance (and helped me troubleshoot it when it wouldn't work). He also tested my generator and his educated opinion is that these units ARE easily capable of producing 12V provided they are in good condition and not overloaded.

Accordingly, I have fitted 12V LED bulbs to everything that would take one which were all the rear and sidecar lights. This leaves me with just a 40W headlamp bulb, a 5W generator warning bulb and the ignition system.

Of course you MUST replace:

  • Your coil if it's a points 6V one. However, the Type III electronic ignition system is rated for both 6V and 12V
  • All your 6V bulbs
  • Battery
My 6V horn is much louder but appears to be okay.

The regulator unit is a Bosch 113-903-803E mechanical unit as fitted to VW Beetles and vans from about 1967 to 1975.

An electronic version is also available, 211-903-803E, which retains the empty case and just mounts the electronic gizmo inside.

You can get one of these new from places like Volkspares for about 21. It will almost mount straight on, but alas, the mounting holes are a handful of cm too narrow, but an extra piece of metal with a couple of holes bolted across sorts that in moments.

I have wired an ammeter into my circuit (on recommendation from Sean). This cost me a fiver. It's the Minda 12V version as fitted to Royal Enfields. The ammeter, wired as my circuit below, keeps tabs on how much current is going to and from the battery.

Anything into positive means that your battery is receiving a bit of charge and all is well. If your battery is a bit low, then it might show a bit more for a short time.

  • If your needle goes all the way over the positive side (8 amps in my case, being an 8-0-8 ammeter) this is about as much as you want coming out of your generator and means that you are overcharging really badly. Stop the bike before you overheat and melt your generator (again).
  • If your needle stays in the negative (and the charge light is on) then you are running on battery power alone and it will be running flat at some point. Either you've dropped below the speed where your generator produces anything (rev it a bit and see what happens, it should move into the positive) OR your charging system has packed up.

Mine seems to run a few amps over positive normally without really much drop with my lights on UNLESS I am idling or running slow. At this point, my generator isn't moving fast enough to produce anything, the needle drops into the negative and I am on battery.

Note that the generator light output on the regulator is not needed as it is on the generator terminal itself.

The regulator contains an extra screw-ring terminal for earth. I wired this to my battery negative. I also have an extra wire from this that runs forward to the headlamp to supply a good earth up there. The sidecar earth, if you have one, can wire here as well.

There are two large spade outputs (B+). They are the same. Take one to your ignition system. Take one to your battery (or via an ammeter to the battery).

I actually found that very few revs would put out the generator light and produce voltage. I'd be prepared to say that the revs required for 12V production are not much more than 6V.

Anyhow, let's see how she goes....

Testing the Generator

Sean also gave me a simple test for generator output. I drew a diagram:  

Basically, all you do is to disconnect all the bikes wiring.

Wire the Field to earth.

Wire a bulb to the generator positive and then to earth.

Start the bike, on battery power obviously, and the bulb should light.

Polarising the Generator

Apparently it is good practice to repolarise a generator when you remount it or after the battery was removed, although there should usually be enough residual magnetism.

This is from the Bosch manual: