Regulator

[Kwkevy]

Morning all
Does anybody have any information about fitting a Wassell 6 volt positive earth dc regulator? The new wiring loom Lucas, ww19105c is very confusing as is the Wassell one . Any help and advice would be most welcome 🙏.  Am a complete humpty when it comes to electrics . I have a 1957 BSA  A7
Much gratitude

[groily]

There are minor differences in the wiring schematic supplied by W and the typical wiring diagrams from back in the day. The forum link here shows two diagrams of the original sort, either of which would (also) be a perfectly good model and might make things a bit clearer for you because the wires are all shown individually from one end to t'other:
https://www.a7a10.net/forum/index.php?topic=8138.0

Since you have bought the W version, it's probably best to follow their schematic rather than unwrap the harness and do it differently.

The W pos earth regulator is designed to operate with the dynamo as it was / is wired for a mechanical regulator, so the picture of the dynamo wiring should not be something to have to think about. The reason W put that info in the package is because dynamos can be wired differently for some other sorts of regulators: it's there so we can make sure, if dealing with an unknown dynamo, that it is definitely wired to suit.

F A D E wires go on the W regulator to correspond with the markings on it. That's to say Green to F, Yellow to D, Purple to A etc as described. If you have the original regulator, you'll see that it's marked F A D E too.
The switch will have its terminals all neatly numbered on the back, next to where the screw posts are. Follow that, and you won't go wrong. The wire from switch position 2 should go to the dipswitch, which then has the separate wires going to the headlamp bulb carrier, for dip and main beam. (The dipswitch may also have the horn push integral with it, in which case there's another wire there which comes from the horn.)

If you break the wiring down, there are basically three elements. Charging, Lights, and Bits and Pieces (ie just brake light and horn usually).

Charging comprises dynamo with its D and F terminals, the regulator with its F A D E terminals, the ammeter which is connected one side to the regulator A via switch T3, and the other side to the battery Live side - Neg in your case. Other battery terminal to earth (Pos).
Lights involve switch terminals 2, 4 and 5.
Bits and pieces - horn and brake light - are taken off the battery. Directly attached for the brake light; and from the battery live wire at the ammeter for the horn. The horn circuit is completed when you press the button, the brake light circuit by its little switch in the power supply wire from the battery.

A WISE PERSON WILL FIT ONE OR MORE FUSES. In the battery Live or Earth lead as an absolute  minimum. 20A rating for 6v systems is generally regarded as a good safe bet. Being sure that it covers the horn and brake light circuits, which are perhaps the commonest causes of grief (along with the equally vulnerable tail light wiring should it chafe under the rear mudguard).

In terms of what specifically goes to what (at the risk of repetition):

It's Dyn D to Regulator D and Dyn F to Regulator F
Regulator E for earth to the frame
Regulator output 'A' - the purple wire on the W harness - to the main switch Terminal 3 and then to the Ammeter. (It's the 'same' wire basically which explains why there are four bits of purple poking out of your harness.  Regulator A could equally have gone direct to the Ammeter, with a link from ammeter to Terminal 3. Same difference. You'll see in the older diagrams that it's done that way, with the one wire on 3 and two on the ammeter that side.)

Only four switch terminals are used -
Power comes in at 3 for distribution as needed according to the switch position;
the feed to the dipswitch and headlight comes off 2,
the front pilot light (only) is at 4 and
the tail and speedo lights come off 5.
The front pilot turns off when the headlight is switched on. That's why it has its separate terminal, but it could equally come off terminal 5 which would make it stay on with the speedo tail light and headlamp, for what little power it consumes.

I think if you match your components and switches to the Wassell schematic (maybe lay everything out on a bench?), you'll find it reasonably simple to figure how it goes together. There aren't all that many wires and the colour coding isn't misleading, apart perhaps from 'Earth T4 and T5' all looking a bit black at the switch end! Dunno why for the Pos earth drawing they didn't use RED for the earths, but there we go.

[Kwkevy]

Thank you for a very expert reply, reading some of the help you have given others on this site , you are indeed blessed with knowledge and experience. 
I have fitted the lucas new loom apart from the regulator, battery and magneto kill switch. With the w regulator there is no purple wire or an A connector, on the w diagram there is a D,F and E . D is the yellow. Green to F . A red to E  with the black wire goes straight to the battery negative via a fuse . Would I be correct in thinking that the w red is the lucas purple and the w E is the lucas A . The lucas black ? Is that sliced into the W black before it's routed to the battery ? Also when I connect the battery according to the Lucas diagram is the black connector labeled earth my positive earth ? And connected positive side of the battery?  And the red connector to the battery negative? . Thank you for your patience.  Kevin

[Kwkevy]

This was the regulator it had on it when I bought it ?

[JulianS]

That regulator looks like the JG 12 volt conversion unit. These needed some rearrangement to the dynamo connections so I would check that the field, D and brush connections on your dynamo are as needed for the Wassell unit.

If I am correct then the attachment is instructions for the JG unit which will show you how the standard connections should have been altered for the JG

[groily]

OK  . . .

 . . . no purple wire on the regulator, that's right. Purple's a loom thing only and is what has to be connected to 'A' from the regulator.
 
At the regulator, there are green (to dynamo F, easy), Yellow (dynamo D, also easy), red (to Earth, positive) and Black which is the live regulated output otherwise known as 'A' which ends up charging the battery. Black's's the one from the regulator that goes to the purple wire of the loom that goes to switch / ammeter and then to the battery. (It could be wired directly to battery negative, yes (as in their simple drawing), and it would charge it, but that would bypass the ammeter and switch which would leave you in the dark as to what's happening.)

So you wouldn't be right in thinking red goes to purple, no. It's the other way round. Regulator RED goes to the black wire shown as E on the loom, and Regulator Black goes to Purple. (This is one reason why the W diagram is rubbish - for Pos earth it should show the earths in RED, while for Neg earth they should be black. But I expect they make one replica loom, and chose the negative earth format in terms of wire colours. Or something.)

Now - and this is VERY IMPORTANT!
The regulator in your picture looks to me to be a JG unit. Not sure, but they were developed in the 1980s originally, to work with Miller dynamos on Velocettes and Vincents. They were, I thought, 12v boxes, with 3 wires off - F and D and A, but no E because the metal box itself provided the earth when it was bolted to the bike. I might be wrong on this, and I only have one very old JG unit to hand to compare - but it doesn't half look like yours! But, the thing is, the JG unit - if that is what you had on there - required the dynamo to be wired differently.
I said earlier you could ignore the stuff about the dynamo internal wiring - but having seen that pic of yours, I think we need to row back on that. Because Miller systems (and in fact all systems bar Lucas just about), required the dynamo's FIELD coil to be wired differently.

Standard Lucas dynamo wiring, for use with their regulators and for most replacements, is that one brush goes to the back of the 'D' terminal. The other brush goes to Earth, attached by a little screw. A wire comes out of the inside of the dynamo, from the Field coil, and is connected to the back of the 'F' terminal. A second wire comes from inside - the other end of the Field coil -and is attached to earth at the same little screw as the brush just mentioned.

That's the configuration needed for the W Pos earth regulator to work.
IF, THOUGH, the one you had IS a JG and it had been installed correctly, then the dynamo wiring will be wrong unless it's been changed already.
For the JG type regulator, the Field coil wires will be connected one to F (as with Lucas) but the other to 'D', NOT earth.
Some folk call this the difference between so-called shunt-wound and series-wound, I prefer to call it 'Live side regulation' (Lucas) as opposed to 'Earth side regulation' - used by most other folk, like Miller, Bosch and a load of others.

SO  . .  as well as making sure that the Regulator red and black wires are hooked up the correct way, I think that after all you need to take the cover off the end of the dynamo and have a look to see how the brushes and field coil are connected. If the two field coil wires from inside the body are connected to F and D rather than F and E(arth), the connections need changing - disconnect the field coil wire that emerges from the bowels of the dynamo from D and connect it to earth along with the tail of the brush that will already be earthed.

If it's already OK, all well and good - but you've got my 'suspicious' genes all fired up and the last thing we want is to screw things up with a basic wiring error.

(Oh, and I see Julian S has raised the same Q  . . . - I doubt we are both wrong!)

Oh again, EDIT forgot to add, yes, for  positive earth it needs the black (earth) wire on battery Pos and the Red wire on Neg. Very counter-intuitive - I'd get some heatshrink in red and black and sheathe the leads to avoid hassle. The loom is designed for neg earth primarily I guess. The regulator for pos earth obviously. It's not that ne'er the twain shall meet exactly - it's just that there's confusion when they do!

[groily]

And this is my own JG 12v + earth one from a zillion years ago. Same as yours as far as I can see.
Still works, but for all that I use DVR2 units these days myself, as do a lot of others on here as you'll have seen.

So, if your bike was working with the JG box and hasn't been touched since, the dynamo wiring will need revisiting. So will the bulbs probably, if they're all 12v. The schematic Julian S attached gives you a pic to follow.