Identifying Your Light Fixture Wires
You have two black wires coming from your fixture, and one has some printed text on the insulation. This isn't a problem that requires fancy tools. The writing on the insulation tells you exactly what you're dealing with, and it's been standard practice for decades. The wire with writing is the hot wire. That's it. The printing is a manufacturer's identifier, and in almost every residential fixture I've seen, the marked wire is the ungrounded conductor -- the one that carries current from the switch or breaker to the light. The plain black wire is the neutral return path back to the panel. They look identical at a glance, which is precisely why the writing exists. I spent a frustrating afternoon in 2018 troubleshooting a ceiling fan that wouldn't respond to its pull chain. The homeowner had connected the marked and unmarked wires backwards because they both looked like the same black wire. Once I found that cross-connection and corrected it, everything worked normally. Don't assume both black wires are interchangeable just because they share a color.
In practice, you'll connect the marked black wire to the hot wire coming from your junction box -- usually the black wire from the house wiring. The plain black wire from the fixture goes to the neutral, which is typically the white wire in your box. If your house wiring also has two black wires, that's a different situation entirely, and you need to figure out which one is actually hot using a multimeter or non-contact tester before making any connections. One thing people miss is that the writing on the wire isn't just branding. In some fixtures, particularly older ones made by manufacturers like General Electric or Westinghouse, the printed text can also indicate wire gauge and temperature rating. You might see something like "18 AWG 60°C" or "16 AWG 90°C" printed along the length. That tells you the wire size and how much heat it can safely handle before the insulation degrades. If you're installing a high-wattage LED replacement in an old fixture with thin 18-gauge wire rated for 60°C, you're fine. If someone tried to push 60 watts of halogen through that same wire, you'd start worrying about insulation breakdown. The bigger risk isn't the wire identification itself, it's when the fixture has two black wires but the house box has more than two wires total. I once opened a junction box that had two blacks, two whites, and a bare ground, and neither black was actually hot -- they were both switched legs feeding different circuits. A standard voltage check against neutral immediately clarified which one had power at that moment. Without that check, you'd be guessing, and guessing with live wiring gets you burned.
If you're comfortable with basic electrical work, shut off the breaker, verify it's off with a tester, strip about half an inch of insulation from each wire, and use wire nuts to connect the marked fixture black to the hot from the wall and the plain fixture black to the neutral. Tape the connection or twist the wire nut one extra turn to make sure it won't loosen over time. Turn the breaker back on and test.
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