Electrical component identification and wiring help

I looked at his water bay pic and YES, the heater is there. Doug

The pic of the snap disc shows 3 wires. BUT just one has a spade terminal. That goes on either side of the Disc. The other 2 do nothing. He needs to look at his heater and follow the wires from the heater. ONE will be ground, probably white. The OTHER will be longer and have another spade terminal and THAT will connect to the open pin on that disc. It got pulled loose somehow. Doug