Questions? Looking for parts? Parts for sale? or just for a chat,

The WD Motorcycle forum

WD Motorcycle forum
Start a New Topic 
BSA wm20 Polarity

Hi Guy's,

Could you help please....?
Are wm20's positive earth or negative earth.
I'm confused which is right and which is wrong if any?
What did they come of of the factory as?
What's the correct Dynamo model number/code for these too please?

Your help is very much appreciated.

Many thanks,

email (option):

Re: BSA wm20 Polarity

Negative earthed as standard, but people do change them sometimes.


Re: BSA wm20 Polarity

As Rob notes the original set up was Negative earth...Using a Lucas regulator box the system can be wired either negative or positive but there is no practical advantage to changing the system...

If you are planning to fit, or already have fitted an electronic regulator, then the bike should be wired to match the specification of the regulator...Electronic regulators are available in either neg. or pos. earth but MUST operate on a system with matching polarity...

If you are changing the system don't forget to alter the battery terminals as well...

Dynamo type is Lucas E3HM...Ian

email (option):

Re: BSA wm20 Polarity

Thank you Guy's,

Your help and clarification is much appreciated.
Mine seems to be wired positive earth when I took the dead battery off and so it seemed a little confusing to me.

Thanking you both again.

email (option):

Nieuwe pagina 1