I hope that someone can help me.
I have just commenced the restoration of my 1950 Lister D 1.5 HP (after a 15 year wait!) and am now on the magneto. I have stripped everything down, cleaned all parts and replaced points and condenser. There is no spark or any sort of output so I suspected the coil. Before replacing this, however, I thought that I do a simple continuity test to check that the moving points were insulated from the magneto body via the insulated fixing post to the condenser and coil.  Well, wherever I put the tester probes it indicated continuity. I checked all the insulating washers etc and all ok. This brought me to the large bakelite insulating block on the inside of the body and the corresponding screw on the outside front at the top. I have looked through all the information I can find on these magnetos but no mention of these parts.
Mine had a large blob of solder which covered the back of the fixing post for the oval plate that holds the moving contact in place and also the back of wherever the screw on the front goes. I thought this looked wrong and removed the solder. I then discovered that I could not tighten the nut securing the oval plate because the post just revolved round - the solder had been holding it in place. I replaced the solder as it was and now total short circuit. I am fairly certain that the problem lies in the bakelite block but I can find out how it's put together or how it's meant to look.
My apologies for the long ramble but any advice would br greatly appreciated.