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I'm in the USA. House was built in 1956. Single pole switch upgraded from 15 amp to 20 amp. The switch has both a white and black wire with no ground.

When I tried connecting the fan/light combo to the existing wires in the attic both the fan/light combo as well as the vanity light would either flicker or was dim even with the switch off. These are led lights. The exhaust fan company told me I couldn't wire them together because they thought my fan had Bluetooth. When I corrected them and told them it was a standard fan THEN they said "Oh yeah our fans can't be wired into any other lights." I find that to be a junk answer. Homewerks brand fan. Any ideas?

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  • What exactly are the existing wires in attic, to switch, and to existing vanity lights? What does each connect to? What is the model number of your fan/light combo? Pictures would help as well.
    – Armand
    Commented Jan 23, 2023 at 6:16
  • only the black wire will go to the switch
    – Traveler
    Commented Jan 23, 2023 at 6:55
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    Is this a new fan, or are you replacing an existing fan?
    – Huesmann
    Commented Jan 23, 2023 at 11:58
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    It sounds like you have a switch loop (with only a black/white pair at the switch). Very common for houses built in the 50s. Please edit your question to provide a pic of the wiring at the switch and the wiring at the ceiling box where you're trying to install this light/fan.
    – FreeMan
    Commented Jan 23, 2023 at 12:49
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    If the lights are dim and flickering even with the switch off a reasonable guess is that you wired the lights and fan in series without the switch in the circuit. Your diagram needs to show clearly the junction boxes and cables. You show the new fan not connected to anything by a cable, you show everything connected at the vanity light (which is possible) and you describe connections "in the attic" but don't show any attic junction box in your diagram. If you draw all the junction boxes and cables we can help you connect them correctly.
    – jay613
    Commented Jan 23, 2023 at 15:10

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If all the wiring is in the box behind the vanity light, you probably have a switch loop so the easiest thing would be to have that switch control both the fan and light.

You'll have to run a cable in the attic, from the fan, down the wall to the vanity light. You may need to replace the vanity light junction box with a larger one to accommodate more wiring.

If the switch will control the fan and light, you use three wires nuts as follows:

  • Power: Black wires from the panel and bedroom, and the white wire from the switch (mark it with black tape).
  • Neutral: All the white wires except from the switch
  • Switched power: black wires from the switch, fan and light

You also need to handle ground correctly. I won't cover that in detail here, but basically all the ground wires should be nutted together and if the box is metal, the one from the panel should be screwed to the box FIRST.

If you want to install a second switch to control the fan you'll need more cabling and the wiring will be different.

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    I was writing my own answer, but yours is good enough, discarded mine. Except: In a proper switch loop, white is actually hot and black is switched hot - the reverse of what you listed. But it isn't always that way, either is possible, and the way to tell is to use an NCVT on the switch to see which wire has power when the switch is turned off.
    – manassehkatz-Moving 2 Codidact
    Commented Jan 23, 2023 at 15:55
  • Thanks, I corrected my answer per your comment. Unintuitive! But seems to be the standard.
    – jay613
    Commented Jan 23, 2023 at 16:06
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    The standard, I believe according to @Harper , is that white is hot because that way if you use an NCVT and the circuit is live you will get a signal from the white, telling you right away that it is "hot". If you use white as switched hot then you might think it is a neutral, and since it wouldn't have power except when the switch is "on", you could get fooled in a dangerous way.
    – manassehkatz-Moving 2 Codidact
    Commented Jan 23, 2023 at 16:19
  • Awesome. Thank you so much. I'm going to take another look at this in a bit. I appreciate everyone's help.
    – Mike Brown
    Commented Jan 23, 2023 at 17:14
  • Let me ask you this... The manual from the fan says I can bundle both white wires together and both black wires together (one set for fan and one for the light). Could I then connect these to new wiring and just connect black to black and white to white in the vanity box?
    – Mike Brown
    Commented Jan 23, 2023 at 17:19

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