I just removed a light fixture which was connected to three wires. One light wire (both are brown) was hooked up to two white wires, and the other wire from the light (also brown) is connected to one white wire. I thought there had to be a black or red "hot" wire in electrical boxes. How should I attach my new light, which has a black, white and ground wire? I am assuming that the two white wires might be my hot wire, but how to know? The ceiling lights and house date from 1990.
If the old fixture worked, at least one of the white wires is hot.
The easiest way to check which is hot is to use a non-contact tester. If the fixture is already removed, leave the two wires bundled together with a wire nut over the end. Put a wire nut on the single white wire. Turn the breaker back on. Only one of those should register on tester. That is the hot side. The other should not register. That is the neutral.
Once you know which wire is hot, mark it with black tape or a permanent marker.
If the the fixture is still attached, you can do the same thing with the fixture hanging down. Once you know what is what, turn the breaker back off before wiring.
The black wire goes to the hot wire, the white to the neutral. The ground wire should be attached to a green or bare wire if there is one in the box, or to the box itself if it is metal. If not, just cap it.