How do you tell the hot wire when both are black?

When both wires are black, you can identify the hot wire using a multimeter or a voltage tester. First, ensure the power is turned off at the breaker. Then, turn the power back on and carefully test each wire with the voltage tester; the wire that shows a voltage reading is the hot wire. Alternatively, if you have access to a ground wire, the black wire connected to the ground can be identified as the hot wire, while the other is typically neutral. Always exercise caution and consider consulting a professional if unsure.