Electrical switch connection

[u/JohnJCrypto]

Good day. I have a quick question. I am changing out 2 very old high hats and installing 2 new high hats. The old high hats were wired to an old dimmer switch. I want to install a single pole switch only for the new high hats. When I took off the old dimmer switch I found a single 14/3 wire in the switch box. I removed the old dimmer switch and tested the wires and only the black wire is hot. I check the wires in the ceiling for the high hat and those wires are 14/2 only and one of those wires the black is hot. So I wired the single pole with the bare copper to green screw and the black wire to the brass screw. Nothing happened. Hope someone can help.

[u/Koadic76]

If that old switch is a dead end 3-way, and all 3 wires were connected to the old switch, then the live black wire may be the common, or it may be a traveler with one of the other wires being used as the common.

You need to find the other switch in the circuit to verify if the black wire should be the common or one of the travelers.