Electrical – Ceiling Light Won’t Turn Off After Replacement

Matching colors is usually correct, but there are exceptions. While this is considered the "right" way, it is for safety issues. The light will work either way. But we don't want the power from the brown going down the blue usually neutral in random parts of the wiring.

Which is why turning off the circuit with the switch is usually safe. If the wiring was reversed, with the switch on the blue neutral, the light will still work, but you would have gotten a really nasty full mains shock, instead of the "little" attenuated by dimmer shock. Always kill power to circuits at the breaker before working on them!

Dimmers, when full off, should indeed be full off. The fact it illuminates a light means it is defective. It needs to be replaced. It's not unusual for dimmers to emit a slight 50 hz hum during use, the volume proportional to the current being passed. But they must be able to completely open the circuit.

If you do get another dimmer instead of a regular switch, do ensure the lamps in the fixture are dimmable, and the dimmer is compatible with the lamp type.

Based on the information you gave, one white/black pair in the ceiling box is the incoming power, and the other white/black pair goes to the switch. You need to determine which pair is which. Connect the chandelier to one pair and turn the breaker back on. If the chandelier lights up, that's the incoming power, and the other pair should be the switch. If you have a continuity tester, you can hook it up to what should be the switched pair (with the breaker off again) and verify that you have continuity when the white and black wires going to the dimmer are touched together. Turning the dimmer on and off may not be enough to get a reading on the tester - the wires need to be touching.

Once the pairs are identified as incoming and switched, the ceiling box should be wired as follows. Connect the incoming white wire to the white wire of the chandelier. The incoming black wire should be connected to the switch black wire, and the switch white wire should connect to the black wire of the lamp. You should also wrap black electrical tape around the white switch wire since it is playing the role of a black wire. This "marks" the wire as black for anyone looking at it later. The same should be done for the white wire at the switch. It should not matter how the wires are connected to the dimmer.

Edit: Now that I search for an image, this appears to be a possible duplicate of: How to properly wire a ceiling light fixture? Which has some handy diagrams. I suspect what you have is the first picture, and what you need is the second picture: