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Jason has used a circuit that effectively takes the rather feeble Hall switch to drive a semiconductor that's capable of handling the heavy current and high voltage spikes that the Buzz box generates.
What do you mean by a magnetic switch, a reed switch or a hall sensor? A reed switch will probably work, a hall sensor will not carry the required current. This is why I built an amplifier module for my vertical engine (mentioned a few posts back).
Do you mean Roger B's post about the amplifier?