Some time ago I lost the mag on my '27 and found the magnets to be very weak. I ran through all of the suggestions from everyone on the forum but could not find any definitive problem that could have caused the mag to die. I replaced the switch, rebuilt the coil box, went though all the wiring, checked the mag pick up and the solder connection, pulled the hogs head to visually inspect the magnets and as much of the coil ring as possible and eventually recharged the magnets in the car using three twelve volt batteries. The result is that the mag is back and putting out 12 volts at idle and 28 volts at fast idle. I still don't know what the problem was and I hope it will not happen again but for now everything seems to be fine!
Thanks to everyone for all the suggestions!
One thing that can zap magnets is to connect Battery DC to the mag post. A bad switch might do this.
That is what I thought and the switch was the first thing I swapped out although I could not find anything wrong with the switch in the car when it happened. That switch had been rebuilt by Ben Martin a few years ago and seem perfectly fine.