There wired in line. One is set to turn off just before 103 an the other is the one you use for your temp control. The Idea is that the main one cycles a lot an is more likely to fail. The second never cycles so less ware an tear. If it fails in the on position the second one will kick the heater off before cooking the eggs. Which one is which is up to you. You could also just put one wafer in it an run on just one with no rewiring but you lose the backup safety. Mine is running with just one now.
