This question already has an answer here:

I can see an answer where it suggests a 3-wire run from the fixture but I'm hoping to use existing wiring and it only has black and white wires coming from the bathroom fan to the old timer switch.

The new modern timer switch has red, white and black wires out (and green of course).

Which wires connect to which wires please?

and thanks Scott

marked as duplicate by RedGrittyBrick, Chris Cudmore, ThreePhaseEel, Daniel Griscom, Machavity Nov 1 '17 at 20:44

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • Can you post a photo of the inside of the switch box? – ThreePhaseEel Oct 13 '17 at 11:44

You got the wrong timer switch. You grabbed one of these digital jobs because you're too cool for school. Unfortunately your wiring is not.

What you need is the trusty dusty mechanical model, available in any "max time" you like. That one's an hour, you can get 15, 30, 2 hours, all the way up to 12.


The black wire on the timer would connect to the power (hot) wire in the junction box, the red wire is the switch leg to power the fan and the white wire is combined with the 2nd wire from the fan and is connected to the neutral wire in the junction box. The green wire is the ground connection.

  • This answer is absolutely incorrect. The OP indicted that he has a simple switch loop without a neutral. All that is coming from the fan is the hot and the feed to the fan. As @Harper answered, this switch cannot be used without a neutral wire. – DoxyLover Oct 13 '17 at 18:17
  • To @ Doxylover: He did not say that he did not have a neutral; he said that he had a black and a white wire coming from the fan, period. .@ RedGrittyBrick stated that this question could be from a duplicate from "how can I install this programmable switch where a neutral is not present". It is not positively known if they are the same question. So in my defense, if the fan has a black and a white wire only, where does that statement say there is no neutral? – d.george Oct 14 '17 at 11:15
  • Let me say one more thing "if there is no neutral how did the fan operate before? Was it devine intervention? – d.george Oct 14 '17 at 12:37
  • If he only has two wires from the fan to the switch, then, as I see it, either (1) he has hot and feed to the fan, or (2) he has neutral and switched, which means the hot to the fan is unswitched, which is illegal and dangerous. – DoxyLover Oct 14 '17 at 18:41
  • if there is no neutral how did the fan operate before?” The neutral is in the fan box, connected to the fan. It can’t be going to the switch if there are only two wires, at least if legally wired. – DoxyLover Oct 14 '17 at 18:43

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