Hello! I have 3 separate pull chain lights in my furnace room all tied to the same cirucuit. I want to install 3 light fixtures and a wall switch. I located where the main power wire comes in and want to connect my wall switch there. How do I wire the wall switch to the that line? Thank you!

..

What else is on that circuit or is it jut those lights?

Good question Bob. I may have to revise drawing.

No, I think your drawing is fine and looks like a tap off the existing circuit. OP just needs to know how and where to tap without messing up anything else on the circuit. We were posting at the same moment earlier

I have 2 outlets on this circuit too. I just don't know how to wire the wall switch to the existing line. All the blacks and whites are already connected on the line.

OK. You have to tell us how the cable is run. Does it go to an outlet, to an outlet, to a light, to a light, to a light?

Or does it go to a light, to a light, to a light, to an outlet , to an outlet?

Or does it take some other route? Are the wires inside the wall and ceiling or are they on the surface?

Hello! The wires are open on the ceiling. The first ceiling box has 3 b&w's all connected. 2 lead back to the panel and one is the line that feeds the other two. The next one in line has an outlet feed, the last is the same with another outlet feed. I want to install the switch to the first box with 3 sets of black and whites.
Thank you!

Are you saying that your wiring looks something like this?

Yes, the only confusing issue is how to wire the switch. Thank you.

You must either change the cable between lights one and two, and between lights two and three to 3-wire cable and wire as shown in first drawing.

Or add another 2-wire cable between lights one and three and wire as shown in second drawing.

Better to use 3-wire cable. You already have 3 cables in first box and the cable to switch makes four. Getting in a fifth will be difficult and will probably exceed code. Unless that ceiling box at light one is very deep you probably should replace it with the deepest ceiling box you can find. Doing so will make your life a lot easier.