Final answer:
The main function of an ignition safety switch is to prevent theft of the boat or PWC by interrupting the circuit and preventing the engine from starting.
Step-by-step explanation:
The main function of an ignition safety switch is to prevent theft of the boat or PWC. When the ignition safety switch is engaged, the circuit is complete and the engine can be started. However, if the switch is disengaged or tampered with, it interrupts the circuit and prevents the engine from starting. This serves as a deterrent against unauthorized use or theft of the boat or personal watercraft.