It's hard to see in the pictures but in the top left corner is where the temperature sensor wires connect. These wires are attached to the hot end with a screw, each attachment screw has two wires that run down and attach to the board. I have ohmed them out and they are not "open".
I have been told that this is the "old" way, the newer ones have a little sensor that is inserted/attached to the hot end. My unit is defiantly the "old" system.
On the bottom row of green plugs, just above the third plug a small red LED lights up continually. The word "overheat" is printed under it and stays on even with all the plug in connectors removed from the board.