I am having an upstairs bathroom remodeled and have a wall opened up that exposes some knob tube that I ultimately want to replace. First, though, I want to understand what's going on.
Fixtures and Switches
1 light at entry of main floor. 1 switch downstairs.
1 light on second floor. 1 switch adjacent to light.
Knob/Tube I can see
2 wires originating from a push button light switch that are in between 2 2x4's Call them L1(left) L2(right)
1 wire that runs full length of opening ( presuming traveling between the 2 light switches ) that also enters the upstairs light switch box. Call this wire L3.
Positions of switches and whether current detected with non-contact current sensor
Dowstairs Switch Upstairs Switch L1 L2 L3 2 lights are
Off On Yes No No Off
Off Off Yes No Yes On
On Off No Yes No Off
On On Yes Yes Yes On
Can someone explain to me what's going on here? I have read about Carter 3-ways and just can't get my head around this.