We just moved into this 1960s era home. In the living room, when the light switch is "off", the wall outlets test ok (both amber lights are lit) using a 3 prong outlet tester. However, when I flip the switch to turn on the ceiling light, the 3-prong outlet tester indicates open ground (the middle amber light stays lit, the amber light on the right goes off). I actually see the amber light on the right edge of the outlet tester go off when I flip the switch to turn on the ceiling light.
What could be causing this? Could the neutral wire and the ground wire be reversed on the light switch? Is this a dangerous condition?