My garage lights are controlled by a single switch inside my house. I wanted to add 2 more lights and have them controlled by an existing switch in my garage that currently powers an outside light. I removed that switch yesterday to begin adding my new circuit, when I noticed that the switch has 2 circuits already coming off of it. One is the outdoor light that I knew about, and the other runs to the existing lights the garage that are only powered by the switch in my house. Is this normal? Can I still add another circuit as I had planned? And can a switch provide constant power to lights that are controlled from a different switch?
Given that the outside lights on this switch are not controlled by the inside switch, there is constant power (unswitched hot) available at this location, and presumably the inside switch that controls the other lights is a switch loop, not their power source. So, you should be able to add more lights on another switch - you just need to correctly identify the unswitched hot supply at this switch location.