Ran into something new today. Got a call that a pilot wouldn't stay lit on a furnace. First thing I thought was thermocouple. I ended up being right but it wasn't as easy as I thought to get to that conclusion. The thermocouple didn't go back directly into the gas valve, instead it was intersected by this small rectanglular device that was wired in series to the limit switch I guess to prevent the pilot from lighting if the limit were to open. Once I figured this out I tested the limit to make sure its wasn't open before replacing the t.couple. Anyone know what that litte f***ing thing is called? Also can anyone explain why on some carrier furnaces (and maybe others) one of the wires coming from the limit has a resitor? I know its so you can't jump the limit out, I learned that by blowing a fuse on the board.