This only applies to the 6 volt dynamo fitted to Ural M63/M66, Dnepr MT9 and the sidevalves
At F2 Motorcycles we get emails about the L414 dynamo not working on bikes that have not been used for a while. 99% of the time there is no need to replace it.
I thought I should share my standard reply to these emails.
It goes something like this.
"You might want to try this on your dynamo.
As it doesn't work you have nothing to loose.
Fit it to the bike and leave everything connected as it should be.
Take a length of spare wire and hold one end on the positive terminal of the battery.
Tap the other end on the backwards facing R terminal on the dynamo.
You will get a flash of sparks each time you tap the terminal.
Do this three or four times.
You may then find that the dynamo works.
The semi-permanent magnet in the dynamo looses the magnetic quality over time.
This procedure re-magnetises it.
It often fixes dynamos that have not been used for a while.
Let me know if it works on yours"
I usually get an email back again saying "thanks, it worked perfectly"
So all I can say is, don't rush out and buy a new dynamo before trying this.