Without knowing where the wires go I would GUESS that the black wire goes onthe common screw.
Sounds like you need a 3 way switch. Your two reds will attach to the two copper screws on the switch. The black will attach to the common screw. Most of the time the common screw is black but not always. It will be a different color than the other two screwsI have a ceiling fan that is controlled at three locations. All 3 locations control the lights and a separate switch(#4) controls the fan. The wiring for switch#1 is 2 red, 2 black, green. Switch#2 is 2 red, 1 black, green. Switch#3 is 2 black, 1 red, green. How do I wire the switch with 2 red and 1 black??
Maybe it happens in San Fran, but I live close to Atlanta.Penisluv?!? Let's just say that I don't live in San Francisco or Atlanta...nor would I want to!