How do I eliminate one 3 way switch and replace it with a single pole switch?

Question

I have knob and tube wiring in our 110 year old house. There are 2 3 way switches that control one light in the house and also supplies power to the garage. There are 4 overhead wires going to the garage so I am not sure if the 3 way in the garage has the main hot wire going to the 3 way or if it is in the kitchen 3 way. How can I tell which one is the main feed and then replace the kitchen 3 way with a single pole switch?

Answer 1

A modification of longneck's process: (not enough rep to comment)

1. Set the switches so the light is on.
2. Turn the breaker off
3. Remove the garage switch; use a test meter to figure out which leads the switch is connecting. Connect those two wires permanently. You are removing this switch from the circuit. Cap the other wire.
4. Remove the other switch; use a test meter to figure out which leads are connected by this switch, hook them up to a single pole switch. Cap off the remaining one.

To figure out where the power really flows in this circuit, you have to power this up safely, with the terminals exposed, and use a neon tester figure out which is hot, when the switch(s are) is off.

Answer 2

You can cheat.

1. Put the kitchen switch in the position that you want to correspond to "on".
2. Flip the garage switch so the light is on.
3. Turn off the breaker.
4. Pull the garage switch out, being careful to not flip the switch. There will be one wire on one side, and two on the other. Connect the single wire to the wire on the other side corresponding to the position of the switch. Cap the other wire off.
5. Pull the kitchen switch out, being careful to not flip the switch. Similar to the garage switch, connect the new single pole switch to the single wire and the wire that corresponds to the position of the switch. Cap the other wire off.