How can I replace a single bulb light with a fluorescent fixture?

Question

I would like to replace a single light bulb light in the closet with a fluorescent fixture. The bulb is wired with two black hots to the light bulb fixture and the white neutrals are wired together. With the power off at the switch and the light off, both blacks are hot. With the switch turned on the light lights up. The switch has typical wiring with neutral white and hot black. This has worked this way for 38 years.

The fluorescent light fixture has the typical black and white (one each) leads to the ballast? Can/should I simply wire the white to a black hot and the lack to black? Doesn't seem proper.

Answer 1

What is probably happening here is you have power to the light on one black, another black to the switch, and a return path along the whites. That is, the switch is AFTER the light.

This is generally unsafe as the light is still energized, even when the switch is off, and should be fixed regardless.

The first thing I'd do is beg/borrow/steel a non-contact voltage detector.

With everything still attached, switch the light off. If I'm right, the detector would read hot on BOTH black wires, and the whites will be un-energized. Flip the switch and the whites should be energized as well.

If this is indeed the situation, the fix is relatively easy. Turn the power off! Remove the existing light.

Figure out which pair is wired to the switch. The easiest way is to use a meter in resistance mode. Find the black-white pair that shows low resistance when the switch is on, and open circuit when switched off. Mark the white wire with a loop of electrical tape. This will be the switched hot.

Now wire the blacks together with an appropriate wire nut, and make sure it's a secure connection. You should not be able to see any copper.

Wire the switched hot (the white wire marked with tape) to the black wire of the new fixture. Wire the remaining white to the white wire of the fixture. Make sure you've grounded the fixture according to the manufacturers instructions.

Mount the fixture, and turn the power back on.

Answer 2

Don't cross the blacks, you're saying you already have a light fixture there that has been happily working and I doubt you plan to rewire the house for this. In that case, simply hook up the fluorescent light the same as the existing light fixture (assuming nothing funky like the single bulb was 220 and you're wiring a new 110 lamp.) If the existing light fixture doesn't have different color wires (both were white or black, etc.) hook the fluorescent black to the black group and the fluorescent white to the white group.

As always, make sure to turn off all power before doing any electrical work and if you don't feel comfortable man up and/or call an electrician.