I'm trying to install a 3-way switch for a specific light but I'm not sure how to do the wiring.
The existing switch box has quite wires inside:
3x 12-2 1x 12-3
The hots (black) are all tied together, the neutrals are all tied together, and the grounds are all tied together.
However, the existing switch has one hot (black) wire connected, and a RED wire from the 12-3 wire.
The light fixture itself only has 12-2 connected (black, white, and copper/ground).
How would I install a second (three-way) switch to this setup?