Worth going through the post John Nash did viewtopic.php?f=8&t=189
on the forum. This should explain most faults/procedures to find out where the fault lies.
There are also Lucas documents on the club website here http://www.arielownersmcc.co.uk/members ... /Lucas.htm
look at the one re Generators. Yours is similar to the E3N
And another good guide to dynamos here https://matchlessclueless.com/electrica ... as-dynamo/
Couple of observations/thoughts:
The WNG was originally negative earth (as were the pre and immediate post war singles). This will not alter whether the dynamo charges or whether the electrical system operates but worth bearing in mind.
Standard Ariel dynamo was clockwise rotation (viewed from the drive end) and the arrow on the body would therefore point in this direction. If (like mine on my WNG) your arrow points anti-clock you have to alter the internal connections (swap the field coil wires). If yours motors clockwise (viewed from drive end) on a battery ( F and D terminals bridges) then the change must already have been made. It is worth checking how the internal wires are connected though for peace of mind.
Here is a post which looks into this https://www.a7a10.net/forum/index.php?topic=12832.0
If the dynamo has not been in use for some time it will need the magnetism reinstating before it will charge (flashing/re-polorising) . Johns post explains how. You need to bear in mind Pos or Neg earth i.e if Pos earth then the positive cable from battery needs to go to the dynamo body and the neg lead briefly touched to the F terminal on Dynamo.
The body needs to have a good electrical contact with the magneto body it is clamped to as this is how the dynamo connects to the Earth side of the electrical system. The bodies were ( I believe) originally Cadmium plated. Any paint on the body will mean a poor or no electrical connection.
Also worth bearing in mind that the Mag also needs a good earth. There is normally a screw terminal lower left side on the points side. I run a wire from this to an engine mounting bolt and /or a separate wire to the main frame earthing point on top of frame under the seat.
And finally...500 rpm is not fast enough to get the dynamo to start charging, you need at least 1000. I use a mains electric drill with a variable speed trigger, my battery drill is not fast enough.
That should be enough to keep you busy for a day