The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: beezermacc on 13.11. 2014 17:20

Title: New Lucas wiring looms
Post by: beezermacc on 13.11. 2014 17:20
Hello! I've just started stocking the new Lucas looms as supplied by Wassells. The looms look very good, braided and complete with the dip switch harness, dynamo harness and rear light harness and the connectors are the traditional bullet and sleeve type. The box is green and white and marked with the modern 'Lucas' logo. Also included is a wiring diagram which is basically a picture of the harness with all the loose ends identified. So far, so good... I sold the first one earlier this week and was subsequently phoned by the customer who is restoring a 1956 Shooting Star. Believing his bike to be +ve earth he was a bit perplexed to find the wiring instructions showing -ve earth. So I checked in the box of another harness on the shelf and the customer is right (isn't he always?), the diagram shows -ve earth (and one or two other issues which don't seem quite right). I thought the A's went over to +ve earth around 1951ish . That's what I've always thought (and not only because it says so in the Haynes manual!). So I phoned Wassells and the guru at Wassells was absolutely adamant that the A's went to positive earth in about 1956, and he said he was quoting from Lucas literature. The box that the harness came out of was labelled A7 / A10 1954 - 62, so even by his admission some would be positive and some would be negative earth. What is the consensus amongst the forum gurus? Am I right or is Humble Pie on the menu?
Title: Re: New Lucas wiring looms
Post by: Greybeard on 13.11. 2014 18:41
My '55 plunger A10 is Pos Earth.

Does the new loom have wired earths?
Title: Re: New Lucas wiring looms
Post by: beezermacc on 13.11. 2014 19:39
Wired earths? Yes, and they are black wires.
Title: Re: New Lucas wiring looms
Post by: Ted_Flash on 13.11. 2014 20:20
Roy Bacon states "For 1951 the electrical system changed from negative to positive earth and remained that way to the end of dynamos for BSA twins in 1963"  (page 102 BSA Twin Restoration)
Title: Re: New Lucas wiring looms
Post by: bsa-bill on 13.11. 2014 20:48
Interesting article here http://www.daviescraig.com.au/POSITIVE_AND_NEGATIVE_EARTH_CARS-news.aspx (http://www.daviescraig.com.au/POSITIVE_AND_NEGATIVE_EARTH_CARS-news.aspx)
Title: Re: New Lucas wiring looms
Post by: beezermacc on 13.11. 2014 22:11
The results of the poll so far  beezermacc 2 wassells guru 0 .  However nobody has yet referred to any first-hand definitive information.
Title: Re: New Lucas wiring looms
Post by: duTch on 13.11. 2014 22:42

 Without putting too much thought in, what is the physical difference between a +ve earth loom, and a -ve earth loom..without even more thought, I'd've just wired it either way...until it was obvious.... *eek*.....Just curious..?...

  I made my own spaghetti....aah sorry- loom, and for what it's worth is +ve E.
Title: Re: New Lucas wiring looms
Post by: Derby Rob on 13.11. 2014 22:43
I seem to recall reading somewhere that originally negative earth was used,then some time in the mid 1950s tried positive earth for a short time before going back to negative earth.

I just cannot think where i read it !
Title: Re: New Lucas wiring looms
Post by: beezermacc on 13.11. 2014 23:46

 Without putting too much thought in, what is the physical difference between a +ve earth loom, and a -ve earth loom..without even more thought, I'd've just wired it either way...until it was obvious.... *eek*.....Just curious..?...

  I made my own spaghetti....aah sorry- loom, and for what it's worth is +ve E.

The wiring diagram that comes with the loom has the earth lead and corresponding battery connection marked -ve, the fuse and wires marked 'power to loom'  marked +ve. An additional issue is that most modern regulators will only work with the wiring earthed according to the regulator polarity, whereas the original regulators didn't mind which way the wiring was earthed. Some of my customers go feint at the idea of tinkering with electrics so anything which confuses them further is particularly unhelpful. However the point of my thread was really only to find out, with some certainty, when the A7 and a10 earth went from negative to positive.
Title: Re: New Lucas wiring looms
Post by: muskrat on 14.11. 2014 07:25
I believe it was the start of the short stroke. BUT in all the wiring diagrams the 1st -ve was with the nacelle headlight. My '51 is +ve.
Cheers
Title: Re: New Lucas wiring looms
Post by: sparx on 15.11. 2014 03:45
The confusion arises purely due to the terminology, the harness is the same irrespective of the earth polarity.
 If the wiring diagram referred to the black frame connections as "earth" instead of -ve and the other cables as (for example) dip beam supply/stop lamp supply/battery supply etc without mentioning anywhere the polarity the problem would go away.
  I suppose another option would be to supply two diagrams or instructions with +ve and -ve swapped over so that, for example, where the -ve earth diagram says "battery +ve" to the headlamp switch the +ve earth diagram would show "battery -ve"
  I have to admit that as an apprentice auto-electrician (many years ago!) I found it very confusing working on +ve earth cars. Fortunately that problem went away with the universal adoption of negative earth.
Title: Re: New Lucas wiring looms
Post by: beezermacc on 15.11. 2014 08:59
Thanks Muskrat and Sparx for your comments. I agree with Muskrat that the A's went to +ve earth, probably 1950 ish coinciding with the introduction of the A10 and shortstroke A7 (this is backed up by Haynes and Bacon - whilst they are capable of getting things wrong they do get most things right). Also, Sparx's comment, absolutely right, if the diagram just marked battery connections as such without reference to polarity that would be fine. However, there are other issues with the wiring diagram, the lighting switch connections are incorrect and the fuse unit supplied isn't shown on the diagram; that latter is only a minor point but customers who are a bit 'electro-averse' need as much help as they can get and any opportunity for confusion needs to be removed. It's much easier to give people a wiring diagram that is absolutely correct than trying to help customers rewire their bikes down the telephone! But my main point was 'When di the A's go to +ve earth?' as the Wassells Guru was absolutely adamant that this happened in 1956, contrary to popular belief. I am, of course, producing my own wiring diagrams to go with the looms. It's a pity about the diagrams because the looms are excellent.
Title: Re: New Lucas wiring looms
Post by: BSA_54A10 on 17.11. 2014 11:11
Ken has what he believes was the first plunger A10 sold in NSW if not Australia.
His 1950 is definitively + earth
Title: Re: New Lucas wiring looms
Post by: trevinoz on 28.11. 2014 06:27
I believe that British bikes converted to + earth as they were fitted with the E3L generator, starting in late 1948?
The AMC singles were a bit different, changing with the demise of the E3AR generator in1951.

Trev.
Title: Re: New Lucas wiring looms
Post by: duTch on 28.11. 2014 10:32

 Ok B-Macc and Sparx, I'm satisfied with that......however.... see photo taken from a 'Ocee Rich' BSA book(Richard L also has one), and note the comment in the red box..??

 My first experience with +ve earth was when I was taking care of my Ma's Austin 1800 and I 'super soft-wired' in a U-beaut Pioneer Clarion(one of the first auto-reverse ones) cassette player, and took a while to figure why all my tapes sounded weird..blew a R/C I/C, also my first experience of the dark science of those, but have just recently they ain't as scary as they seem.. *eek*
Title: Re: New Lucas wiring looms
Post by: chaterlea25 on 28.11. 2014 20:08
Hi Dutch,
We would if we had a mirror *????* *????*

John
Title: Re: New Lucas wiring looms
Post by: olev on 30.11. 2014 00:24
Gday Dutch,
I think Ocee means the negative ground circuit is not interchangeable between models (A, B & M).
The previous page (P78) shows the circuit for positive ground A & B models.
Its a good book, isn't it?
cheers
Title: Re: New Lucas wiring looms
Post by: kiwipom on 30.11. 2014 08:27
hi guys, yeah Dutch how we supposed to read it, cheers
...P.S. Back in NZ now pity we couldn't have met up, but had those `fauch and chuups `at the: Maloolaba fish market, Parkyn Parade, they were the best. 
Title: Re: New Lucas wiring looms
Post by: duTch on 30.11. 2014 08:51


  Hmmm- dunno how that happened, maybe this piccie will help..I found a mirror *smile*

 Yes Olev, mine came with my first Beeza, the Road Rocket, and I don't have to use it a lot, but it's good for all kinds of otherwise obscure info.
 I did see the other page(s), but figured that was the most 'relevant'- but still a little vague....

  yo K-P... yup, sorry 'bout that I got caught short with various goings on and couldn't get along, maybe next lap

 oh yeah I'll try and sort that pic out... *computer* *dunno*
Title: Re: New Lucas wiring looms
Post by: Bob Moyes on 15.07. 2015 14:50
I have a 1951 Plunger A10 which is positive earth