Replacing 2 wire switch with 4 wire switch, box has 3 wires. Help?
The black wire from the box, old switch, gets connected to the black wire from your new switch with a wire nut. The red wire from your old switch gets connected to the red wire from your new switch with a wire nut. The white from your new switch gets connected to the group of white wires under the yellow wire nut, those are the neutrals. I can't tell if there's a ground wire in the box from the cables or if it's FMC. Verify the box is grounded with a meter going from box to black (hot).