Note that it has two black wires. The live circuit wire will light up the tester.

How To Replace Gang Plate On A C Bus Light Switch
How to disconnect a light switch. Turn off electricity at the circuit breaker by turning the circuits breaker switch to the off position. Turn off the power to the switch at the main circuit breaker or fuse panel. Then use a voltage tester to make sure that the circuit is dead. Pull the switch out. Remove the screw that secures the switch faceplate to the fixture using a screwdriver of the correct type. How to disconnect a wire from a light switch.
Unscrew the cover from the switch using a flathead screwdriver. To replace this kind of switch follow these steps. Unscrew the switch from the electrical box using a phillips screwdriver. Unscrew and remove the switch plate. You only need simple tools and materials to do this. The project should take less than 30 minutes and cost less than 3.
When you have distinguished the wires turn off the breaker and remove the other wire from the terminal. Set it to any position aside from the test position and flip off the switch that the light is connected to. Unscrew the switch from the electrical box and pull it out with the. A switch on the fixture should read on time usually found directly under the motion sensor. You need a slotted screwdriver two wire nuts a blank light switch insert or blank wall plate and possibly some electrical tape. If you are unsure find the switch by testing all the available switches before you fiddle with the on time button.
To disable a light switch remove the two wires from the switch and tie them together with a wire nut. With the power off of course. Gently pull the. Turn the breaker back on then test the leads on both switch terminals with a voltage tester. Disconnect the wires at the switch if you plan on permanently removing the light.