How do I Wire a 120V Indicator Lamp?

Use a commonly available neon induction probe to test the AC source for which you will install an indicator light. Test which leg is actually wired "hot" (the probe will light), and make a note.

Unplug the device you are wiring with the indicator, or if you're working with a hard-wired connection like a wall switch, turn off the breaker or take out the fuse for the circuit.

Cut the hot-side wire between the switch and the device you are powering. Strip back 3/4-inch of insulation on both sides of the cut. The indicator light fixture usually comes wired with stripped ends, but if not, strip those, as well. Wire-nut the cut ends together with one indicator wire.

Repeat Step 3 with the neutral return wire and the other indicator lead. If you are wiring the indicator to a wall switch, wire one wire end under the neutral wire screw and the other under the switched-side screw, along with the wires that are already there.

Flip the circuit breaker on or reinsert the fuse. Test the indicator by flipping on the switch. If it does not light, try changing the bulb. When everything works, mount your indicator light in place.