There are two types of ice makers, those in which all of the parts can be individually replaced and those in which some of the parts are clustered together into a control module. To determine which model you have remove the outer face plate. If there is knob, pull it off first, then pry off the face plate with a small screwdriver.
Before testing the shutoff switch, unplug the refrigerator to avoid an electrical shock hazard.
Modular units have holes in the module's face plate for test probes. If you see several holes, each marked with a letter, it is a modular unit. Component units (like the one shown below) usually have exposed gears and don't have holes for test probes.
Modular units do not use a separate shutoff switch. Instead follow this link to view instructions for checking the shutoff