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#717761 - 12/05/17 8:33 am Electrical question BSA A65 1970  
Joined: May 2017
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Chess Offline
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Sverige
Hi everyone!

I'm just about to start rebuilding the electrical system on my A65 -70. But I have a question, some of the posts I've read here on britbike suggest that the BSA's have a positive earth, is this true on my -70 as well?

Regards
Christian

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#717762 - 12/05/17 8:37 am Re: Electrical question BSA A65 1970 [Re: Chess]  
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Shane in Oz Online content
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Shane in Oz  Online Content
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Yes, they were positive earth in 1970.

#717763 - 12/05/17 8:39 am Re: Electrical question BSA A65 1970 [Re: Chess]  
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Stuart Online content
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Hi Christian,

Originally Posted by Chess
some of the posts I've read here on britbike suggest that the BSA's have a positive earth, is this true on my -70 as well?

Yes. As standard, all BSA's had been "positive earth" for many years by the time your A65 was built, and continued to be "positive earth" until the last in 1972.

Hope this helps.

Regards,

#717766 - 12/05/17 9:08 am Re: Electrical question BSA A65 1970 [Re: Chess]  
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Chess Offline
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Sverige
Oooh how interesting! I've not worked on a positive earth system since my Jaguar many years ago.

Just to be absolutely sure; that means that when I'll connect the "earth" on the battery I'll connect it to the positive terminal on the battery?

It would be a shame to fry the system :-)

#717771 - 12/05/17 12:31 pm Re: Electrical question BSA A65 1970 [Re: Chess]  
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gavin eisler Online content
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gavin eisler  Online Content
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argyll. scotland, uk
Yes, positive terminal on battery is earth/ground on most BSAs, red to frame.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#717851 - 12/05/17 10:04 pm Re: Electrical question BSA A65 1970 [Re: Chess]  
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Chess Offline
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Sverige
Perfect! Thank you all for your help! Didn't manage to get started on the actual building of the system today. But I enlisted the help of a couple of friends, some coffee and, what we swedes call, an strössellängd to try to get my head around the electricity of it all! It took three engineers and one opera stage set builder but we managed to get get it mostly sorted. I discovered that I am missing a couple of pieces that need to be ordered so I can continue building!

#717859 - 12/05/17 11:03 pm Re: Electrical question BSA A65 1970 [Re: Chess]  
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gavin eisler Online content
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argyll. scotland, uk
The earthing scheme can stand a little improvement, run a red earth wire from the rear lamp bulb holder frame back to the main earth point, the rear lamp needs it, something similar for lamp bucket and coils if using EI. The original scheme uses the chassis to make the earth to the rear lamp , not a great idea.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#717863 - 12/05/17 11:18 pm Re: Electrical question BSA A65 1970 [Re: Chess]  
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koan58 Online content
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Or if you're starting from scratch or a lot of repairs to do, consider a single point ground approach. It may already have most of that anyway.

#717895 - 12/06/17 9:22 am Re: Electrical question BSA A65 1970 [Re: Chess]  
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Chess Offline
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Sverige
It has no electrical system at all as it is now. So I am replacing it "from the ground up" so to speak.

I've been planning to run an extra earth to the rear light as I don't trust the rear fender as an conductor, so to speak. Thank you for confirming my hunch!

When you talk about a single point ground, do you suggest to eliminate the frame earth all together or just make some kind of extra junction point to put the "big earths"? Do you recommend using some kind off connection block?

#717898 - 12/06/17 9:51 am Re: Electrical question BSA A65 1970 [Re: Chess]  
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Stuart Online content
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Hi Christian,

Originally Posted by Chess
When you talk about a single point ground, do you suggest to eliminate the frame earth all together

That is not possible; there must be at least an 'earth' wire to the engine, as components like the spark plugs, oil pressure switch and points 'earth' through their mountings on the engine. Then, because the engine is not insulated from the cycle parts, by definition, they are 'earthed' too. Nevertheless, if you use standard rectifier and Zener diode, they also 'earth' through their mountings to the frame; ideally a Red earth wire is attached to these mountings so, again by definition, the cycle parts are 'earthed'.

Some believe that Single Point Ground means each electrical component has its own 'earth' wire all the way to the aforementioned Single Point - for example, to that point on the engine. In practice, this is wasteful and over-complicated.

Because your bikes does not have any electrical system, it depends how you intend to proceed - an off-the-shelf harness will/should contain the standard Red 'earth' wires network that connects most electrical components (except the rear lamp) to battery +ve; if building your own, I would be happy to describe the network I developed 35 years ago and have used on all rewires since.

Originally Posted by Chess
I've been planning to run an extra earth to the rear light

Risking stating the obvious, run the 'earth' wire alongside the Brown and Brown/Green wires to (respectively) the brake and tail filament in the bulb. At the rear lamp, if the hole those two wires pass through into the lamp is large enough, run the 'earth' wire beside them and solder the end to the bulb holder. However, if the hole into the lamp itself is too small for a third wire, terminate it with a 3/16" (5 mm.) i.d. ring terminal one one of the 2BA studs that protrude from the rear lamp through the rubber backing pad.

Hth.

Regards,

#717912 - 12/06/17 1:53 pm Re: Electrical question BSA A65 1970 [Re: Chess]  
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hopski Offline
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WALES
Originally Posted by Chess
Perfect! Thank you all for your help! Didn't manage to get started on the actual building of the system today. But I enlisted the help of a couple of friends, some coffee and, what we swedes call, an strössellängd to try to get my head around the electricity of it all! It took three engineers and one opera stage set builder but we managed to get get it mostly sorted. I discovered that I am missing a couple of pieces that need to be ordered so I can continue building!


I've not long rewired an A65T project and the off the shelf Lucas main wiring harness was ok up to a point due to the cheap connectors supplied so I ran separate earths wherever possible to the frame especially the headlamp circuits and rear brake light on the advice of the good folks here. I couldn't even get the speedo lamp to work until I ran a separate earth to the speedo bracket for some reason.


BSAOC South West Wales Member
#717928 - 12/06/17 3:56 pm Re: Electrical question BSA A65 1970 [Re: Chess]  
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DMadigan Offline
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ca, us
Single point ground are mainly used on audio, RF and high power systems to prevent ground loops caused differences in potential between separate grounding points. The only place this is significant on a motorcycle is when an electric starter is fitted. If a separate ground is used for the other parts and the starter ground becomes a high resistance the starter current will go through the separate ground and overload it. Putting a fuse on each non-starter ground wire will prevent this.
Presuming a starter is not being fitted, four ground wires would make it more reliable - engine, tail lamp housing, headlamp housing and Zener diode. Later looms used a rectifier ground wire also because they were bolted to a painted surface.

#718003 - 12/07/17 7:51 am Re: Electrical question BSA A65 1970 [Re: hopski]  
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Stuart Online content
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Hi,

Originally Posted by hopski
I've not long rewired an A65T project and the off the shelf Lucas main wiring harness was ok up to a point due to the cheap connectors supplied so I ran separate earths wherever possible to the frame especially the headlamp circuits and rear brake light on the advice of the good folks here. I couldn't even get the speedo lamp to work until I ran a separate earth to the speedo bracket for some reason.

By "not long", "Lucas" and "cheap connectors", you mean a Wassell Lucas harness of the usual Wassell quality? smile

Ime, 'original Lucas' harnesses had a single Brown/Green wire to speedo. (and tacho.) bulb holders, with a separate Red wire terminated with a small ring terminal for attachment to one of the speedo., or bracket mounting fasteners. The modern pattern harness builder omitted the Red wire?

Similarly, headlamp shells had a loop rivetted to the bottom of the shell that took an original harness Red wire with a bullet terminal on the end. This was not as good a headlamp return as a similar loop for another Red wire actually on the BPF headlamp bulb 'cap' itself but I'm not sure all had the latter.

Regards,

#718073 - 12/07/17 8:09 pm Re: Electrical question BSA A65 1970 [Re: Chess]  
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Andy Higham Online content
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Bolton Lancs UK
When I wire a wire a bike any connections to earth are purely accidental


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc grasstrack
2003 Aprilia RSV Mille "Lo Stregone"
#718111 - 12/08/17 4:30 am Re: Electrical question BSA A65 1970 [Re: Andy Higham]  
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quinten Online content
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quinten  Online Content
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the ground side
is just an extension of the battery terminal
connected to that side.
in this case, an extension of the (+) plus terminal for positive ground.
the voltage potential is or should be the same , +/- 0~2 percent
accross the battery, near the battery and away from the battery. .. on this side of the harness.


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