On an engine with magneto ignition, I have a hard time grasping how magneto ignition coils would affect anything in the electrical circuitry. All they do is detect magnetic pulses generated by a magnet in the flywheel, amplify it, and send it to the spark plugs. No connections to the rest of the system except a for a kill wire from the key switch.
I'd be more prone to take a good look at your battery or charging system. My
