How do I properly wire the replacement dimmer switch when the box has more wires than expected for single pole

Question

I thought my over head light switch only controlled my overhead light. It is a dimmer switch that no longer dims so I want to replace it with a dimmer that will function.

When I removed the wall plate and examined the switch I saw that it had 1 ground wire 1 red wire and 2 black wires. There are 2 capped off white wires in the box. One of the black wires is hot (I confirmed the hot wire with a voltage meter) and this hot wire was pushed into the back of the switch. The red wire and the other black wire each were screwed on brass screws located on the same side of the the toggle dimmer switch.

The replacement dimmer switch I purchased is a Lutron Ariadni dimmer which should be compatible with incandescent, LED and Halogen lights. I attached the dimmer by screwing the black hot wire beneath the black screw, and the ground wire beneath the green screw, I connected the remaining red and black wires to the 2 copper screws on the side of the new switch. When finished I discovered that this switch evidently operates more than just the overhead light because after I installed it 2 other light fixtures (both hang from the ceiling and have their own wall switches) stopped working correctly.
If I turn on the overhead light I was replacing the switch for, that light works just fine and dims when I dim it, but the other 2 lights can no longer be turned on.
If I turn off the overhead light I replaced the switch on the other 2 lights work just fine. One of these other light fixtures also has a dimmer switch which works fine.

I have no idea what the next step needs to be to get this to work properly. Help would be greatly appreciated.

Answer 1

Lutron Ariadni LED+ Dimmer AYCL-153P-BL is a 3-way switch, so it does need to be treated differently from the old 2-way toggle.

The single black screw that you found on the new switch is correct for the hot wire. However, I can't tell from Lutron's instructions if that one screw is designed to hold more than one wire. To be on the safe side, get a wire nut and about 6" of black wire and splice those three black wires to make a pigtail connection to the black screw.

The red wire seems to provide the switched power to the light in your scenario. Connect that to the brass screw, the lone screw on the one side opposite the black screw. This is important because the other brass screw would cause the switch to operate upside down.