Forum

[R Evans]

I need some help with converting a 1976 Indian Ex Army Bullet to 12v. BIke is genuine & original and nice people and DVLA have just given me age related number. I have a 4 wire alternator and rotor and new 12v harness etc . On trying to fit this evening I found the Woodruff key on the crank is wider than the slot on the rotor so I know something is wrong but unsure where to go next, sort of committed to the conversion, any guidance gratefully received!

[John-M]

Have you bought replacement parts? I would expect to find a 3-wire alternator on an early Bullet.

The 12V conversion involves connecting 2 of the three wires together, then the two wires to the rectifier/regulator.

[R Evans]

Hi, yes I bought replacement parts ( maybe the wrong ones) The bike had no electrics with it at all so I thought I might as well do the conversion. Currently have new 4 wire alternator and 12v new style wiring harness, which wires should I link together on the alternator? Am i right in thinking that if I do this I probably also need to change the new rotor to one that has a wider slot so the current woodruff key will fit? Appreciate any help, many thanks

[Adrian]

The 4 wire alternator first appeared around 1999 and is intended to power the headlight separately from the rest of the electrics via its own direct 12V AC supply (the yellow and orange wires) avoiding the battery and charging circuit altogether, while the two purple wires (or possibly red and black) are linked to the reg/rectifier unit for supplying power for everything else. This needs different switchgear for the lighting and is fine so long as you have the engine running, but if you want the all the lights to be able to work with the engine off you'll have to use a different system. Before 1999 there was a 12V system more like the mid 1960s Lucas early 12V set-up on British bikes with a three wire alternator, but I can't remember which two wires were permanently connected.

It is possible to connect the wires so that all of the 4 wire alternator's output is passed through your new 12V regulator/rectifier, which will need some other small mods to the rest of the wiring. The Pete Snidal Bullet manual has details as well as all the relevant wiring diagrams.

If you can get a refund on your 4 wire alternator I'd be tempted to get a Lucas RM21 or Sparx 005 two wire job.

As for the rotor key, if you do stick with the 4 wire alternator I'd buy one to fit the wider slot in the crankshaft and file the top half to fit the rotor, or else open out the slot in the rotor to fit the wider key.

A.

[John-M]

Further to the above, a 12 volt conversion on old British bikes with 6 volt crank mounted Lucas alternators retained the original alternator and was a wiring exercise rather than a replace exercise.
The alternators have six coils and on the 6 volt systems four coils were used for general running and other two were switched in when the lights were being used. This was because old voltage regulation was poor and unable to cope with all six coils when there was no demand, preventing blown bulbs and boiled batteries.
When modern voltage regulation came along they used the same alternators but used all six coils all the time to supply 12 volts. The alternators will actually put out 20 volts-ish, but the regulator/rectifier tames this down to 12 volts.
These older alternators have three wires, some modern replacements for these have two wires, but are effectively the same.
The 3 wire alternator should have three wires coming from it, Green/Black-Green/Yellow-White/Green.
The Green/Black wire and the Green/Yellow wires are connected together and are connected to one of the yellow wires on the Regulator/Rectifier. (The two wire alternators effectively have the Green/Black wire and the Green/Yellow wires connected.) The White/Green wire goes to the other yellow wire on the Regulator/Rectifier.
The two yellow wires are where the (AC) power goes into the Regulator/Rectifier and the red and black wires are where the rectified (DC) regulated to 12 volt comes out, red + black -.
I'm not sure how the 4 wire alternators would be connected, other than the fourth extra wire is, as said above, is an AC feed for the headlamp, and doesn't go via the regulator/rectifier.

[Adrian]

John,

think of the 4 wire alternator as having two PAIRS of wires, one pair for the AC headlight via its own AC regulator, the other pair to go the the reg/rectifier to provide 12v DC for all the other electrics.

What does not help at all is that some 4 wire stators have red and black AC wires for the feed to the reg/rectifier, which can be misleading as the DC supply FROM the reg rectifier ALSO uses red and black wires as you mentioned above. In this case the red and black wires form the stator connect to the two YELLOW wires on the reg/rectifier, however counter-intuitive it seems. If the 4 wire stator has two purple wires it's easier to remember to connect these to the yellow wires on the reg/rectifier.

A.