How to test a dimmer switch?

Testing a residential electronic wall dimmer switch to determine if it has failed internally involves checking line voltage continuity and output performance using a digital multimeter. First, always ensure safety by shutting off the corresponding circuit breaker at your main service panel and testing with a non-contact voltage tester to confirm zero power. Second, remove the wall plate and disconnect the switch wires. Third, bypass the dimmer temporarily by wire-nutting the incoming hot wire directly to the switch-leg wire leading to the light fixture, then restoring power at the breaker. You can troubleshoot lighting faults safely. You can verify that your test is successful when bypassing the dimmer makes the lights turn on normally at full brightness, proving definitively that the dimmer switch itself is faulty and must be replaced.