There are 3 switches in a downstair room and there are 3 bulbs in an upstair room. How do you determine which switch is connected to which bulb by only going upstair room once? You don't know the status of the bulbs on the downstair. 더보기 Turn on the first switch and the second switch and leave it on for a few minutes. After some time, turn off the second switch go to the upstair room, and inspec..