The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Stephen Arsenal on 10.12. 2010 15:56

Title: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: Stephen Arsenal on 10.12. 2010 15:56
Charge ? control ?
L Live/Line
Hi guys,was told this is an old BSA switch,it fits perfect into the divers headlight mounting.I´m trying to fix the wires into the back,but is proving very difficult .
There are markings on the rear,L,+D,H,T,SH  (not sure what +D stands for)?
Any suggestions would be welcome
Any directions of which coloured cable goes into which clamp,would be even more helpfull.Not sure if there needs to be a bridge between two of the clamps-cheers-steve
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: iansoady on 10.12. 2010 16:42
At a guess, Charge, Light (side & tail), Headlight.

Those switches can drive you mad. For the one fitted to my Velo which was similar (but slightly different) I found the best solution was to draw up truth tables for each switch position and note what connected to what with an ohmmeter for each position. Took time but eventually gave me the correct connections.
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: bsa-bill on 10.12. 2010 17:11
Oh yes - been there
Could not work out how it could possible work, my old Flash switch is similar but has an internal connection which explains how it works once you discover this fact.
the one I was using had no such connection but was supposed to have an external one (little arm connects one terminal with the centre pin ) but this was missing so much head scratching went on until I eventually bought a new switch and all became clear
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: Stephen Arsenal on 10.12. 2010 17:21
Thanks,why would there be a charge switch ? what has that to do with the bulbs ?
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: chaterlea25 on 10.12. 2010 17:56
HI Stephen,
The charge position switch is pre 1936/7 when the CVC regulator appeared
Before that the "C" position fed the field coil through a resistor (sometimes mounteo on the back of the switch)
When the lights were turned on the field coil was connected directly,
The supply for the field coil came from an adjustable third brush in the dynamo

HTH
John O R
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: groily on 10.12. 2010 18:19
Could it be because it was originally for a bike with an unregulated 3 brush dynamo Stephen?
In which case, you'd expect to link D, via the switch, to a feed for the field coil(s) to support loads or cope with a flat battery? Lots of varieties (with various levels of subtlety) of the genre, but all primitive compared to the sophistication of a '50's BSA!
See, just for example, what Austin Seven cars used in the pre-war era: www.da7c.co.uk/technical_torque.../threebrush_dynamo.htm
Might explain the D connection on the back? C on the front face could be Charge, or maybe 'Control Brush'.
No matter - Ian's 'truth tables' will have it doing the things you need, if you want it to, whatever it really is!
(Just seen John's post . . . there we go)
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: Stephen Arsenal on 10.12. 2010 18:32
Thanks for your quick replies,so in a nutshell,I ignore the +D clamp un the rear,and the C position switch on the front,and make a truth table ?.My fame is a positive,but the switch is isolated anyway,so should´nt be an issue ?As I have only 4 wires,in theory I should only really find the main cable power source(which I think goes from the battery,to the tailight,and back up the fame to the switch)??.Anyway,thanks again..this switch is the bees knees,it has a deep throated click,each time its switched ,and is quizte heavy too,nice piece of work .
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: Stephen Arsenal on 11.12. 2010 12:49
Thanks guys,everything sorted,took a while ,contact roller was´nt connecting sometimes because of ingrained hardened old grease on the blind side the screw clamps.
Title: Re: Can anyone tell me what the letter C and L stand for on this light switch ?
Post by: wilko on 11.12. 2010 21:50
I knew that!