ml magneto no spark

Doe,s any one know how to test a magneto? the mag off my lister B is an ML and its got no spark, I have stripped and cleaned the points and reset them and I have fitted a new HT lead, I have used a test meter on continuity and the points stay live open or closed, and there is no continuity between the points and the HT lead, I hope this makes sense to some one and they can point me in the right direction. Thanks, Pete.

Test the resistance between the HT lead and the magneto case. It should be about 4000 ohms. While this is not definitive, it indicates that the HT part of the coil might be OK. Significantly higher or lower figures would suggest a duff coil.

Thanks I will give it a go in the morning