Identifying whether a 3-way light switch is defective involves observing operational symptoms or conducting diagnostic multimeter checks. Common warning signs include lights failing to turn on unless both switches are in a specific matching position, intermittent flickering when toggled, or a switch handle that feels loose and fails to snap firmly. To test definitively, shut off the breaker, disconnect the wires, and use a digital multimeter set to ohms to check continuity between the common terminal and traveler terminals across switch toggles. You can troubleshoot switch wear easily. You can verify that your diagnosis is correct when a multimeter showing infinite resistance or failing continuity confirms internal contact failure, proving that you must replace the faulty switch.
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