I want to replace a light switch in my home with a dimmer.
Each switch has one wire going into the wall and the other pigtailed with the corresponding wire from the other switch.
I am testing with the lights off.
I want to figure out which is the hot and which is the load wires before removing the old switch.
I have never used a multi-meter with AC power and the one I have is not very fancy. When I test the 2 terminals on the current switch, I get around 105 V (I guess there is something wrong with how I am making contact). When I reverse the leads, I still get the same value, not the negative.
I wanted to make sure the box is properly grounded. I thought that the single wire going into the wall was the hot; but there is no voltage difference between that wire and the box. There is a difference of 120 V between the pigtailed wires and the box. Again there is no difference when reversing the leads.
Are these pig-tailed wires hot and the single wires load?
The wiring diagram from the dimmer's instructions:
The wall box has 2 light switches in it: