I have a switch that only controls the kitchen light. It has a ground wire, two black wires and a red wire. The red wire connects to the kitchen light, but one of the black wires seems to sends power to the dining room light so a single pole switch doesn't allow for the light in the dining room to work. I also randomly attempted a 3 pole switch but you cannot have both the kitchen and dining room lights on at the same time.
Since you appear to have 2 cables rather than 3 (3 would be incoming power, light fixture, dining room), you likely had something like the following:
- Power goes first to kitchen light - black hot, white neutral
- At kitchen light, black incoming to black 3-wire cable, whites together (and to fixture neutral), red of 3-wire cable to fixture hot (aka switched-hot)
- In switch box, 3-wire cable has black hot, red switched hot, white neutral
- In switch box, 2-wire cable has black hot and white neutral for dining room
In this scenario, the blacks go together to one side of the switch, the red goes to the other side of the switch, whites go together (but don't connect to the switch unless it is a smart switch that needs neutral).
However, any color except white can be hot or switched hot. So there is no definitive answer to which wire is the actual unswitched hot wire. You need to figure that out. You may be able to do that with a non-contact voltage tester, and you can double-check and be sure with a multimeter. (Carefully!)
There are really only three possibilities:
- Black of 3-wire cable. If that's the case, blacks together to switch, red to other side of the switch.
- Black of 2-wire cable. Unlikely here, but technically possible. That would mean the feed to the dining room is actually through the 3-wire cable, with hot and neutral carried on from the fixture box to the dining room. And if that's the case, again blacks together to switch, red to other side of the switch.
- Red of 3-wire cable. If that's the case, red goes together with the black that is not in the 3-wire cable on the switch and the black (in the 3-wire cable) goes to the other side of the switch.
On rereading the question, I see a key phrase: The red wire connects to the kitchen light
Assuming that is 100% definite, that would match either the first or second scenario. In either case, that means blacks together.
Blacks together (or any two wires together on a switch) can be done one of 4 ways:
- Backstab + screw. Not recommended.
- 2 wires under one ordinary screw. Not allowed!
- 2 wires under a screw-to-clamp connection.
The all-purpose works with any switch answer is a pigtail. That's three wires (more sometimes) in a wire nut, with one of those wires being a short piece (black or red or yellow or blue or any color not green or white if hot, white if neutral) of wire that then connects to a screw on a switch or receptacle. This makes life much easier when a switch is replaced.
If you, at some point, decide to put in a smart switch, timer, motion sensor, etc. that requires a neutral, then you will need to use a pigtail (add a white wire to the existing neutral bundle, might need a new wire nut).