Locate the detergent cup. The photo below shows a close up of a dual style detergent cup and the bimetal assembly. The dual style uses a bimetal switch for each cup. In the picture, the cup is open. If it were closed, the lever arm (partly out of frame) would swing down and lock into place in the bimetal assembly.
Before testing the switch, check the alignment of the assembly by latching the cup closed. With a small screwdriver, gently push the metal until the detergent cup opens. Some assemblies can be adjusted to improve the alignment. If the alignment does not appear to be a problem, then remove the assembly and test the switch.
Label the wires and connections so that you can properly reconnect them later. The wires are connected with slip on connectors. Firmly pull the connectors off of the terminals (do not pull on the wire itself). You may need to use a pair of needle-nose pliers to remove the connectors. Inspect the connectors and the terminals for corrosion. If either is corroded they should be cleaned or replaced.
Use a continuity tester or multitester to test for continuity. Set the multitester to the ohms setting X1. Touch one probe to each terminal. The switch should have continuity. If it gives a reading of infinity, the switch should be replaced.