Testing Overhead Light Fixtures With a Multimeter

Position a stepladder under the light fixture. Ensure that the ladder is in the fully open position, based on a flat, non-slip surface and positioned so that you can work on the fixture without leaning to either side.

Remove the existing light bulb and place it somewhere safe where you cannot fall onto it. Do not place it in a pocket or hold it between your teeth.

Ensure that the building's power supply is on, and that the switch for the light is in the "On" position. Check the power supply by switching on other lights or appliances in the room, and check the switch position by comparing it to others in the area.

Switch on the multimeter and set it to measure AC voltage. The meter switch will indicate either "AC" or the international symbol for AC -- a short wavy line. Unless the meter is an "auto-ranging" model, select a voltage range that is greater than the anticipated lighting voltage. For example, if the lighting system runs on 110 volts, select 220 volts on the meter dial.

Touch the two meter probes to the two contacts within the light fixture bulb holder. It does not matter which probe goes to which contact, so long as they do not touch each other. Observe the meter. If a voltage akin to the anticipated one registers on the display, then the light fitting is working. For example, if the lighting uses 110 volts and the meter reads 108 or 112 volts, the light fixture is fine.
If the meter shows a negative value don't worry. It means that the probes are the wrong way round. Either swap them around so they touch the opposite contacts in the bulb holder or just ignore the minus sign. Only the number is important.

Move the meter probes around on the surface of the contacts if the meter fails to detect a voltage. If this does not result in a reading, swap the probes between the contacts and try again. Finally, if there is still no reading, reverse the position of the light switch and try once more. An absence of voltage, or a voltage much lower than it should be, indicates wiring problems between the power supply and the light fixture.