Before you pull the magneto, pull the kill wire off the side of the unit. It's not the uninsulated braided ground wire that's also attached to the mag body, but the insulated wire that has a nutted connection to a screw in an insulator, that sticks directly out the side of the mag, looking right at you.
If the key switch failed, it could be grounding-out the mag. If that proves to not be the problem, there's something that failed catastrophically to cause the no-spark. Ign points don't normally fail while the engine is running.
Not uncommon for the rotor to short out internally, so be sure to check for spark right off the coil, to the mag body, when you get it apart.
A relatively safe way of doing that is to lay the mag on the workbench, ground the shaft of a medium-to-large screwdriver against the alum. mag body, and hold the tip approx 3/8" away from the copper strip coming off the top of the mag coil.
Give the magneto shaft a sharp turn clockwise, and a strong spark should jump the gap. If it's orang-ish or won't jump, inspect points etc for problems. If the spark will jump off the copper strip, but doesn't get thru the rotor/cap, strongly suspect problem with the rotor. Clean the cap while the mag is apart; carb cleaner will flush out any crud/deposits.
2 other things I've seen that cause instantaneous ign failure are cracks/shifting of the insulator in the side of the mag case, where the kill wire connects. Also a "blown" coil; look for cracks and/or arc marks on the exterior of the coil. You may have to pull the coil from the magneto housing for a full inspection. Cut the safety-wire on the coil's lock-screws, loosen screws then remove coil.
Points are gapped to nominal .008". The mag driveshaft has a flat machined into it, and will only fit into the mag drive one-way. You'll find that there's a very small slot machined into the bottom circumference of the mag drive and this gives you a visual cue for orientation of the flat.
HTH, let us know what you find..........ed
