I agree taking a hose to the roof may help you find the leak but I think I would climb up there and look at all my vents, ac, antennas.... If the caulking is cracking get some Dicor lap sealant and go at it. Check around all the windows too, still use Dicor but not self level for sides. After you have done all that then pull the hose out or next rain be inside looking.
You said it was coming in thru a light switch so it's in the wall before you see it at the switch..... That's why I would caulk the heck out of it first and then check, no need to let more water in. When it stops maybe try to look behind and see if there's any damage or extra clean up needed. Maybe just to fix and dry out will be fine. Good luck!