They are 2 common types of ignition switch. There are a couple other less common ones with a 6th terminal, but they basically work similar.
One is for battery powered ignition, and one for electronic, magnetron type igntions. The magnetron does not like when 12 volts is sent to its kill wire by the wrong type keyswitch. Sounds like thats what may have happened on your first one.
The terminal on the keyswitch that goes to your magnetron, needs to have continuity between the terminal and switch body or G terminal when off, and no other position, and it can NEVER have 12 volts on that terminal. It also can not have continuity to any other terminal, except the G terminal if there is one.
If your keyswitch does not have a terminal marked M, its probably for a battery ignition (they usually have a terminal marked I instead of M).
IF you have a service manual or wiring schematic for your machine, Bolens shows the terminals that are connected when the key is in various positions, and what each terminal does, and where it goes in the harness. Can be very helpful so you can wire up your new switch to match, once you are sure you have the proper type switch.