Remove the adjustment mechanism it's often part of the bracket holding the switch in place! As for identifying the pressure switch, that's easy. Nine times out of 10, it's directly behind the 'water level' adjustment knob in the top control panel of the machine. If the machine's upside down or partly destroyed, follow the sensing tube from the base of the wash tub. And while you're at it, it's also usually worth scrounging the tube, which is often a high-quality plastic hose. You never know when it might come in handy.By contrast, dishwasher pressure switches are normally buried beneath the stainless steel drum.
Typically, washing machine pressure switches have a large sensing diaphragm that's about 60mm or so in diameter and three quick-connect male terminals. One connection is common, while the others are for normally open (NO) and normally closed (NC) connections. A set-point adjustment mechanism is built in (it's directly controlled by the 'water level' knob) and the switch opens and closes with audible clicks.