I've replaced light switches before for regular "black, white, ground" setups and 3-way setups. So I was helping a friend who asked me to replace a switch/receptable combo with just a plain on/off switch. I opened up the existing switch/receptable combo and found an extra wire - a red one! I figured it was either a traveler for an old 3 way (I was guessing; no 3 ways were ever seen) or an extra hot. The unit looked like:
SWITCH (top) (toggle left>right) 110 V receptable (bottom)
It was wired like this (the 2 screw terminals on each side):
-- RED BLACK -- | -- WHITE nothing -- (ground at bottom)
I figured white was neutral because it was the only silver screw and the only one labeled on the back to be "white". I didn't have a meter but I had a basic "light goes on" continuity tester. I did "black to white" and the light went on. "Red to white" and the light didn't go on. So I capped off the red one and wired up the new "just plain on/off" switch with "black to white", plus the ground. Flipped the house circuit back on and it popped with a spark. I tried another switch and it did the same thing. I figured it was obviously my wiring but I didn't know why. I put the old switch back together and decided to post here! What am I doing wrong and what the heck is the black wire and the red wire?