Last Updated on September 1, 2017 by Dave Farquhar
If you’re changing out a light fixture and find two wires on the fixture and three wires in the box, you’re not out of luck. Here’s how to connect a 2 wire light fixture to a 3 wire ceiling box.
Safety first
Always turn off the power at the breaker or fuse box before you work on electricity. This keeps you safe from potential electric shock.
Map out your wires
First, map the wires coming out of your electrical box. The white wire is common, going back to the electrical box. The black wire is a hot wire coming from the box. A red wire is an alternate hot, often coming from a light switch. A bare or green wire is ground.
Black, white, and green or bare
If you only have three wires coming from the box and one is the green or bare wire, your job is easy. Tie off the green or bare wire with a wire nut. Connect black to black and white to white. You’re done. Connecting ground is a very good idea, but not necessary for the operation of the light.
Multiple other colors
When you have other colors involved, such as blue or red, it gets trickier. Always connect white to white. The question becomes which of the other wires is hot or switched. Some junction boxes have always-hot lines present, in case you want both a switched light fixture and an electrical outlet.
Unfortunately the only thing you can do is map out the wires with a multimeter or experiment. If one wire is always hot, that’s not the one you want. You want the wire that’s hot when the light switch is on, and registers zero volts with the light switch off.
If you don’t have a multimeter, connect one of the non-white wires to the black wire on the fixture. Turn the power back on. If the light always stays on, you picked the wrong one. If the light switch doesn’t work, you picked the wrong one.
What to do with the extra wire
After you determine the correct wires to use, put a wire nut on the end of the wire you don’t use. Then wrap a piece of electrical tape around the end. That way the wire can’t short out, and if you ever need to use it, just remove the tape and wire nut and the wire will be ready.
Further reading
While you’re updating your light fixture, why not think about modernizing your lighting too? I’ve had good experience with LED bulbs.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.
I have a 3 wire, black, white & ground ( power) connecting to a switch coming into the box, a 4 wire, black, white, red & a ground coming from the bathroom ceiling fan into the box & I would like to add a 3rd switch for my light above the medicine cabinet, how do I connect the power source to the 3rd switch. I connected the whites together, run a black to the light switch & run a black pig tail from the light switch to the fan switch & a red wire from the fan source to the top of the light switch, it seems to work fine but my problem is hooking up my wires to the 3rd switch. can you please help me? Greatly appreciated…..
That’s a more ambitious project than I will typically undertake. I think what you’ll need to do for the third switch is run another independent wire to the light above the medicine cabinet, and connect that independent wire to the switch, along with a second black pigtail. Running that independent wire to the medicine cabinet would be the hardest part by far.