Stop walking across a dark room to turn on the light. Install a 3-way switch and control lights from two locations.

1. The scope of Art. 404 can be found in Sec. 404.1. When wiring 3-way or 4-way switches, only the phase conductors can be switched [Sec. 404.2(A) and (B)]. As a conductor for switching purposes ...

My house was built in the 50s, with wiring ... modern switch is 2 blacks marked hot, a white marked neutral, and a grey marked gnd. It seems like maybe the existing switch is a 3-way switch?

In the diagram on the link they are using a three conductor cable after the first three way switch. Black ... They shared the white neutral wire. It sounds like you got it figured out, but ...

Wiring for 3-way and 4-way switching must be done so that ... The white insulated conductor within a cable assembly can be used for single-pole, 3-way, or 4-way switch loops if it's permanently ...

(For more than two locations, add 4-way switches ... Below, I'll show you the most common way to wire a 3-way switch. It's what most electricians use today, because it's easy and saves money.