Generally, replacing bulbs or fixtures is the extent of a service professional’s duties with respect to lighting. However, occasionally, the light won’t come on – is the problem the breaker, the cord, the fixture or the bulb? To narrow it down, try the following steps.
1. Visually inspect the fixture. Remove any color inlays from the lens. If there is any water, cloudiness or black soot, the bulb has probably burst and will need to be replaced.
2. Turn off the power at the breaker. Open the J-box and expose the wires. Sometimes the gasket fails, allowing the box to fill with water, which will short out the wires. Clean and thoroughly dry the box.
3. Turn the breaker and light switch on and use a multimeter to verify power is getting to the light fixture cord. If not, trace the issue to the breaker or switch. Sometimes there is more than one switch, or a remote control. The second switch may be off.
4. If the breaker trips when the light is turned on, disconnect the light cord from the power wiring at the J-box and reset the breaker. If it continues to trip, the problem is with the breaker or GFCI. Rarely, the wires between the breaker and J-box have shorted together. If the breaker stays on, the fixture or its wiring have an issue.
5. Test the circuit continuity with a multimeter. Touch one lead to the white wire of the fixture cord and one to the black. If there is continuity, the bulb and wiring are OK.
6. Using the multimeter, touch one lead to the green and the other to the white, then to the black. If continuity exists between the white and green or black and green, the wiring is bad. Test the bulbs similarly: touch one lead to the threaded part of the bulb base and one lead to the tip of the base. A good bulb will have continuity while a bad bulb won’t.
Credit: Swimming Pools, Spas, Hot Tubs, Fountains, and Similar Installations: Mike Holt page 14: Article 680, based on the 2017 NEC.