I recently had a new roof put on, and the installers pulled out the old attic fan, leaving the thermostat box. At the same time, I noticed my lightpost outside has stopped working... so I went up in the attic to check the state of the wiring. There is 3-wire feeding into the old attic fan thermostat. For safety purposes right now, I simply disconnected everything and capped them off, but I'm thinking I likely need to actually connect some wires together here to keep the 3 way going. Attached is a photo of what the wires looked like when I found them. I think there was a white wire from the old fan connecting to the white from the line but it simply got ripped out entirely.

My question is how do I proceed in connecting potentially 2 of these wires here. Knowing that isn't the safest thing to do, I didn't want to take any chances.

attic fan thermostat wiring

  • By lightpost you mean one attached near the roof of the house? I don't see why a post in the yard would be on the same circuit as an attic fan. Was your attic fan really 240V? Don't see why there would be 3 wires going to it. The red and black tied together after the switch would seem like a short to me if the switch turned on. Do you have a breaker tripped?
    – topshot
    Oct 7, 2016 at 17:27
  • correct, i'm not 100% sure the lightpost outside having an issue is related or not, but as you likely know people wire things oddly before it's your house :) The 3 wire usage is confusing to me also. No breaker tripped. I'm really just trying to be sure this thing gets terminated properly.
    – shawnwall
    Oct 7, 2016 at 17:38
  • Maybe your bulb is out? It appears the black wire heading out the box on the left is just bare so that could be an issue if there's ever power on that red wire or the switch turns on. I'd flip the breaker, verify with a meter nothing on black or red to ground and then totally remove the box. Then disconnect the 3-wire cable at whatever junction box it comes from. If none are in the attic, leave the switch but disconnect and cap the 3 wires individually and replace the cover.
    – topshot
    Oct 7, 2016 at 18:36
  • Where does the red wire in that /3 NM coming in from the right go to? Oct 7, 2016 at 22:50
  • @topshot The bulb outside isn't out. I tried changing the bulb go no avail.
    – shawnwall
    Oct 8, 2016 at 15:52

1 Answer 1


Everything on the left side of the box is wrong, this isn't a simple matter of what to connect together. I don't know if it was the roofers that messed it up of if it was wrong to start with. However all conductors must be inside sheathing [or conduit or a box] at all times, meaning that the cable sheathing must come slightly inside the box and the cable clamped at the entrance or within 6 inches of the entrance. Second there aren't enough conductors on the left to do anything. Keep them all disconnected and capped separately.

To solve the lamp issue start with the lamp fixture and switch, test the wires for voltage, if it has power change the bulb if no power trace it back until you find power. This requires a meter of course, no practical way around that.

  • old post i'm coming back to: the lamp post outside has nothing to do with this. the wire is hot leaving the house to that lamp. it must be broken underground.
    – shawnwall
    Jan 26, 2023 at 16:46

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