4 Wires: 2 Hot. What to do?

Did you buy a "Three Way" dimmer switch?

Originally I had a single prong--but I'm going to get a three way. I still don't know how to wire it with the four options. How can there be 2 hot wires? What's with the two wires twisted together (red and black)?

You should have made a diagram of the way the original switch was wired and connected those wires to new switch. Most 3-ways' have one screw that is different color or marked in some way to identify it as the "common" connection.
BTW - If you put a dimmer in only one location the lamp will only be dimmable when that switch is providing the power.

I agree, I should have. But I didn't. What to do now?

How are the wires grouped at the back of the box? (Which cable does each wire come out of?) Are there any white wires?

Two white wires, twisted and tied off with electrical tape.

The two wires (red and black) that are twisted together come from the top of the box--out of the left hand corner. (These seem to lead directly to the light fixture itself as it's above the box.)

Two wires that tested "hot" (black wires that are separate) come up from the box.

There was a small "jog wire?" (small piece of black wire) attached to one of the wires as well and it was attached to the old switch.

(I really appreciate all of the questions and help. Thanks for taking the time to read!)

Stacie said:

Two white wires, twisted and tied off with electrical tape.

The two wires (red and black) that are twisted together come from the top of the box--out of the left hand corner. (These seem to lead directly to the light fixture itself as it's above the box.)

Two wires that tested "hot" (black wires that are separate) come up from the box.

There was a small "jog wire?" (small piece of black wire) attached to one of the wires as well and it was attached to the old switch.

(I really appreciate all of the questions and help. Thanks for taking the time to read!)

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You should get a small pack of red wire nuts.
Remove the tape from the two white wires and place a wire nut over them;
The two black wires are probably the travelers that come from the other switch. They would go to the switch one on each gold colored screw.
The red and black that are twisted probably had the jumper that went to the black screw on the switch. Use a wire nut to connect the jumper.

Thanks, that helps a lot. I think I get what to do with the two black wires.

"The red and black that are twisted probably had the jumper that went to the black screw on the switch. Use a wire nut to connect the jumper." I want to make sure I've got this part right. I should use the jumper (the small black wire that's attached to nothing) and twist it with the red/black wires (already twisted together) and then connect it to the black screw. Correct?

Do you think it's a problem that there is no grounding? It's an hold home (built in the 20's) so I understand that many of these older homes don't always have grounding at every outlet, but I don't want to cause a fire due to my ineptitude.

Your plan sounds right. Ground has nothing to do with switch power.

Great! Thanks again for the help--and I'll remember to take a photo of the wires and label them next time.

-Stacie

Done. Correct?

Okay, I bought a 3 way dimmer switch and rewired. The switch is currently installed but a small buzzing noise is coming from the outlet when turned on.

Here's how the wiring ended up:

Red and black wires that are twisted together I twisted the jumper cable to them, capped it, and then connected the wires to the copper screw. The two hot wires I connected to the two gold screws on either side of the switch.

(There are four screws on the switch. One green, two gold, and one copper.)

Did I do this correctly? The switch works but I want to make sure I didn't wire it correctly before putting the plate on.

hello, that "red" you said showed up on your tester was probably a 30 to 40 volt bleed over from your other three way switch. i don't know for sure why but when you have a three way circuit there is around 40 volts always reading on a meter when the light or device is off. you need a volt meter that will read voltage to find your true hot wire. a tester that just lights up won't work for a three way circuit. thanks, budro

Thanks Budro--do you think that I still wired it properly or should I switch it off and buy a voltage tester?

Stacie said:

Okay, I bought a 3 way dimmer switch and rewired. The switch is currently installed but a small buzzing noise is coming from the outlet when turned on.

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What are you referring to as the "outlet?" Is the light fixture that these switches control mounted in a ceiling?

Nope, not ceiling. I'm using incorrect language. Buzzing is coming from the light, or around the light, on the wall above the switch. It might even be coming from the switch itself but it's hard to tell as they are very close. It only happens when the light is dimmed, when it's fully on the buzzing is gone.

Stacie said:

Nope, not ceiling. I'm using incorrect language. Buzzing is coming from the light, or around the light, on the wall above the switch. It might even be coming from the switch itself but it's hard to tell as they are very close. It only happens when the light is dimmed, when it's fully on the buzzing is gone.

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Try changing the lamp inside the fixture.
Cheaper lamps can cause a dimmer to buzz.

if it's humming, shut the power off to the dimmer or disconnect a wire till the buzzing stops and we can talk tomorrow. yes, you need a volt meter you can read numbers on. harbor freight has them for about three dollars. a week or two ago they were giving them away as a door gift. thanks, budro

i just read jbfan's reply. he could be right. i didn't know it was okay when on all the way. if you have a newer curly q bulb that may be your problem now. thanks, budro

Buzzing from the switch is normal with "old" dimmer's, as in not digital. Does the buzzing go away when the light is at full brightness? Buzz's when it's dimmed?
If so it's the internal resistor built into the dimmer that's buzzing.