The holding switch is located on the mounting plate, near the central cam. The holding switch can be differentiated from the water inlet switch by the thick spacer which raises the holding switch off of the mounting plate. Also, the holding switch uses three wires, while the inlet switch uses only two.
Remove the switch by removing the two screws that hold it in place. The switch is connected by three wires. Label the wire placement on the switch before disconnecting the wires. The wires are connected to the switch with slip-on connectors. Firmly pull the connectors off of the switch terminals (do not pull on the wire). You may need to use a pair of needle-nose pliers to remove the connectors. Inspect the connectors and the terminals for corrosion. If the connectors are corroded they should be replaced.