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I have a malfunctioning fluorescent light over my workbench and I want to replace it with an LED fixture. (I'm pretty sure the fixture is still getting power because I got the slightest jolt when I tried to swap out the fluorescent tube and momentarily made contact with one of the tombstones. There is also the slightest flicker when I replace the fluorescent tube and turn on the fixture.) The fixture is VERY old, probably going back 50 years. As far as I know, it has never had any maintenance done on it. (It's the house I grew up in and someone in our family has lived there continuously.)

I realize I could probably solve the problem by replacing the ballast resistor but even if I chose to do that, I'd need to turn the power off to the fixture to do that. So how do I determine if I've turned off the appropriate breaker WITHOUT touching the tombstone with my finger again?

I have a small digital multimeter with probes but I'm not sure where to touch the tombstone with it or how to set the meter to verify that the fixture is live.

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    The fastest way if you do not know the breaker and the light does not work is to turn off the main breaker. No guessing, no getting shocks. The other way is to find another light or receptacle on the breaker and turn off breakers till you find the right one.
    – crip659
    Commented Sep 2 at 13:50
  • @RMDman Concept is correct. But knowing how much nasty stuff there is on Amazon (Harper can tell you all about it if you don't believe me), please stick to known reputable brands with UL or ETL or similar listing such as Klein. Still easy/fast to get from Amazon but with a tested/verified/safe design.
    – manassehkatz-Moving 2 Codidact
    Commented Sep 2 at 14:18
  • Intention was only to make the OP aware of the tool. My though is the OP would purchase where they went to buy the ballast or the new fixture. Will fix the post.
    – RMDman
    Commented Sep 2 at 14:27
  • Do yourself two favors. Buy a non contact circuit tester pen and replace the entire fixture. It will probably be less than the ballast.
    – RMDman
    Commented Sep 2 at 14:28
  • You'll never get another fixture of that quality. Consider converting it to ballast-bypass direct-wire LED tubes. It's easier than you realize.
    – Harper - Reinstate Monica
    Commented 2 days ago

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If there is a full documentation package it might include a floorplan of the house with designations of which breaker every fixture is on. Or the labels on the breakers are good enough to figure it out.

Given that your house is ancient (and probably has some DIY done to it) the best way is to start flipping off breakers until the fixture no longer has power.

Use a voltage tester to ensure the power is actually off. You can use a multimeter on the voltage setting.

First see that it works by turning on the light and seeing that you get a hit, then flip breakers until you no longer see voltage, flip that breaker on again to see if the power gets restored. Then flip it off again to work on the fixture. This makes sure your tester didn't die on you while checking the breakers.

Potential places for the probes are one on the place where you got shocked from and the other on a ground or neutral. Between the connections of the tube. On a typical tube there are 2 pins on each end, check voltage between the ends with all combination of pin locations. Between the place you got shocked from and one of the ends (again check all pin locations).

If you don't want to deal with all that mess, turn off the main breaker and use a portable battery powered light to do the work.

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  • I think the OP understands all that, but doesn't know where to apply the probes for the voltage tester.
    – RMDman
    Commented Sep 2 at 14:03
  • @ratchetfreak I've ordered the Klein non-contact circuit tester and it's overdue now. In the meantime, I was hoping for a really clear description of where to put the probes if I did want to determine if the fluorescent light is getting power. (I've removed the tube.) The ends each look like this: ( | ) but I'm not sure where to put the probes of my multimeter.
    – Frank Lee Speeking
    Commented 2 days ago

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