Replacing a very old 3way switch

Question

I’m attempting to replace a very old 3way seitch.

It has four terminals: top two are black and white, and the bottom only has one black connection. I suspect the upper black wire is power because it is shared by a jumper to the top of a light switch that only connects to a bulb.  What are the roles of the other wires?

I’m attempting to connect to a Honeywell RPLS540A/RPLS541A dusk dawn timer. This requires 4 wires:
Yellow for 3way switch
Green for ground
Black for load
Black for line

What wires from the existing switch should I wire into my new device?

Additionally, I see a copper wire at the back of the box wrapped around a screw. The box itself is metal. Is this my ground wire?

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Corinne Stroum 1 year 1 Answer 266 views

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