The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: bl**dydrivers on 09.12. 2017 01:02
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I know the switch I need is Lucas 31340, I have an original, but it’s missing parts and the new replica ones have a different layout underneath.
What’s missing?
Can I use parts from a new one?
Want to keep the switch original.
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If you do a search, you should find previous threads about this.....if I can remember I'll do it later too
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Probably no parts missing from your original switch.
There are at least 2 versions of the switch.
Terminal 5 - for tail and speedo light needs a fixed contact between the terminal for headlight and the terminal for pilot light.
On your original you will probably find the contact is internal , an internal brass contact in the bakelite between 5 and the brass sleeve in which the rotor moves. Test with a meter and you will probably be able to see the end of the contact if you carefully examine the switch near 5.
First photo is such an original switch.
The pattern switch - ignore the pressed brass bits you dont need them - it has an external contact between 5 and the rotor.
On the original Lucas switch with external contact the stud in terminal 5 was locked with solder.
Second and third photos show an original Lucas switch with external contact.