Morning all
I am making good progress on my recently purchased B31 but am struggling with the electrics, every wire would seam to be connected to earth?
both leads to battery when using a continuity tester go to earth. All wiring diagram's I can find are for later models any ideas? >:( >:(
Sounds like a short
Have you made your own wiring loom or are you using one 'off the peg"
In which case which make and which diagram are you using?
This might be useful for you (BSA Service Sheet 808A):
https://oldthumpers.wordpress.com/wp-content/uploads/2012/02/808-wiring-diagrams.pdf (https://oldthumpers.wordpress.com/wp-content/uploads/2012/02/808-wiring-diagrams.pdf)
In this case you would normally disconnect each component one at a time with your meter attached to discover which one is shorting.
ps here is a negative earth version:
(https://scontent.fltn3-2.fna.fbcdn.net/v/t1.6435-9/53615591_877817229216396_7574671754212147200_n.png?_nc_cat=106&ccb=1-7&_nc_sid=13d280&_nc_ohc=v8E0VHr6zW0Q7kNvgEB8H-n&_nc_ht=scontent.fltn3-2.fna&oh=00_AYAH6ZOBF8InN2haqyVwZATYjrAtC4XCDrtnqrElMkk_rg&oe=66C8354D)
This is the loom layout for the above:
(https://degroot-bsa.nl/wp-content/uploads/cm/data/DeGroot/8654933.JPG)
As Neil says, and your bike is negative earth.
Derek & Neil
Thanks for the reply, most useful. The loom is the one that was on the bike when I got it.
I am very surprised it is negative earth, I have worked on and own many old bikes and all of that ilk and all were positive.
I have been connecting it positive.
That diagram will certainly help.
many thanks
Bunners
BSA bikes, and probably most others, were negative earth up until about 1952 when they changed to positive earth. This followed motor industry practice at the time, when it was believed that positive earth systems were superior and reduced corrosion.
I quote this from the Austin Healey Owners magazine.
"... Cars built after the late '60s used the negative pole of the battery as ground to the chassis. Negative ground was also used on all British cars up to about 1936.
At that time, it was found that there were certain advantages to grounding the electrical system via the positive pole, and the practice was applied almost universally to British cars for over 30 years. There were two main advantages: grounding the positive side of the supply makes the polarity of the central electrode of the spark plug negative, resulting in improved plug performance and longer service life for the plug and the high-tension cables. Positive ground also reduced the formation of electrolytic sulphation at the positive battery terminal lug, and also reduced electrical leakage from battery cells to ground as a result of acidulated moisture. Positive ground also reduced corrosion at points, connectors and soldered joints, especially under conditions of high humidity."