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I am replacing fluorescent light fixture. The previous owner had 2 fluorescent light fixtures connected with a single switch. Those lights stopped working. I checked its not the tubes that were just bad. So Home Depot Associate said that probably the ballast were bad and suggested to replace the fixture with LED style fluorescent fixture.

So I took one of the fixtures off. It had 2 sets of black, 2 sets of white and 2 ground wires coming into it. In my wisdom I put caps on 1 set and connected the other set to the light. This did not work . So I was going to try the other set. But decided to search as why I have the 2nd set.

Q1: Based on the google search it seems like that the 2nd set is to connect the 2nd fluorescent light fixture. So I am thinking to connect both sets of wires to the 1st fixture. Thoughts?

Q2: I am also having some thoughts as what is the possibility that 2 sets of fixtures have gone bad at same time. May be I should do something else.

The house is build in early 1990s

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    You have very typical parallel wiring. Your "sets of wires" probably went from the switch to the first fixture and then to the 2nd fixture. That they both failed at once tells me the switch or another connection may have gone bad. "Back stab" switches and outlets are notorious for failing. With the power off remove (DON'T DISCONNECT) the switch, take many pictures. You may need to do some sleuthing to figure out what happened, but bear in mind, nearly all electrical problems occur at connection points, which is why the code requires them to be "permanently accessible" .
    – George Anderson
    Commented Dec 29, 2020 at 15:51
  • Ballasts do burn out. It's possible both are bad. Use a voltage tester at the first fixture to verify power.
    – ojait
    Commented Dec 29, 2020 at 17:02
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    This might be a switch leg if you try the other set and after you turn the breaker back on the light stays on then it probably is let us know and we can tell you how to wire it to get your switch working again. Yes it is common for ballasts to fail , many leave the lamps well beyond there life (50% point) and this is hard on the ballast. If you were just using the switch to turn the power off check your breaker panel you may have tripped a breaker.
    – Ed Beal
    Commented Dec 29, 2020 at 18:04

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If you originally have (2) black wires and (2) white wires coming into the existing light fixture ,that had been working before, than these are connected to the new fixture.

The black wire from the new fixture connects to the (2) incoming black wires and the white connects to the (2) white wires.

It might be wise to replace both fluorescent fixtures rather than keep one and replace the other with an LED.

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The myth of "spare" wires

Novices often discover more wires in a box than they think they need for their immediate project.

Their line of thinking goes "Well, since I don't need them for what I am doing right now, therefore they must be spares".

Not at all. Spare wires are extremely rare in electrical. Builders are cheap, and will generally only install the wires that are needed right now. The only exception I know of is "switch loops" where neutral is now required (for benefit of smart switches), and it took a Code change to finally force builders to even do that! That means EVERY wire has a purpose and a job.

You found them connected, they better stay connected

Those "extra" wires actually have a very important job. You don't know what it is, so don't break it.

A lamp only hooks up with 2 wires (not including safety ground, which is simplicity itself). It's pretty hard to mess that up :)

If you see the old lamp's 2 wires going off into a tangle you do not understand, you are probably better off snipping them off halfway up their length and using them as "pigtails" to the new lamp. That requires owning a wire stripper of course.

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