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Help! Replacing single light switch with digital timer

Posted by misterz (My Page) on
Fri, Nov 13, 09 at 8:48

I thought this would be an easy install but once again am wrong.

I pulled the single standard light switch circa 1985. There are 3 wires. 2 are black with no markings and the third is metal wire. One of each of the black wires go into top and bottom holes again with no labeling and the wire to the side connection.

The new timer has 4 connections; black/hot, white/neutral, green/ground and to make it more confusing a red wire.

Can I do this myself or am I going to need to bring out an electrician to replace a single fixture? Man, im bummed.

Thank You!


Follow-Up Postings:

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RE: Help! Replacing single light switch with digital timer

You need a neutral (white) wire to run the timer. Your box just has a switched hot and the bare wire is a ground. You need to find a way to get the neutral from that circuit to the box where you want to put the switch.


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RE: Help! Replacing single light switch with digital timer

Thanks. On closer inspection. There are a lot of wires in there. Not sure why there are so many.

From the light switch...top black wire leads to a black, white and brass wire going up thru the wall to the left.

From the light switch...bottom black wire leads to what looks like a splitter with 2 black wires leaving it.

One of the black wires leads to a black, white and brass wire going up thru the wall to the right.

The other black wire leads to a black, white and brass wire going down the thru the wall somewhere.

The metal wire leaving the light switch appears to be connected to all 3 brass wires mentioned above.
And all 3 white wires mentioned above are capped together.

Jeesh. Who would have thought a single on/off light switch it could have so many wires.


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RE: Help! Replacing single light switch with digital timer

Jeesh. Who would have thought a single on/off light switch it could have so many wires.

The light switch only cuts one black wire, the rest are just passing through.

Each set of white, black and copper wire is a cable.

One cable coming in to the box is from the main circuit panel providing power.

One cable going out is the feed to the light.

The other cable going out is to other outlets or switches and has nothing to do with this switch or light fixture, it is just passing through.

The timer is both a switch and a fixture so you need a neutral besides cutting the black/hot line.

Black to incoming hot black.

Red to black going to the light fixture.

White to the other whites.

Copper to the other copper.


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RE: Help! Replacing single light switch with digital timer

Thank you very much for taking the time to reply. Gives me a much clearer picture of what is going on in there.

I guess my problem now is with no labeling on any of the blacks and not knowing where they are coming/going. How do I know which is the incoming hot black...And which is the black leading to the light fixture?

There is no labeling...and I have no idea where they are coming or going in the back of the wall there.

Is there some trick to figure out which is going to the light, which is the hot/circuit and which is passing thru?


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RE: Help! Replacing single light switch with digital timer

Where you took out the old switch is the hot in and the black to the light. Remove the old switch with the breaker off. Clear everyone out of the room and turn the breaker back on with the wires positioned so they don't touch anything. Using a tester, touch a probe on one black wire and the other probe to the ground, and the same for the other black line. Whichever lights the tester is the incoming hot.

You have two free black wire ends, that goes on the timer.

The white must go on with the other whites.

The ground must go on with the other grounds.

All you need to know is which black is incoming hot and if you are wrong you only have to swap the wires to the black and red on the timer.


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RE: Help! Replacing single light switch with digital timer

Got it.

Im going to assume the bundled blacks is the incoming hot and the single black is leading to the fixture. If it doesnt work ill just swap it.

Thanks again for all your help....much appreciated.


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