For a receptacle assembly used as the switch base for cigar lighter and power outlet, the contact between the thermostat and its mating device is analyzed by introducing a simple model involving two spring-loaded rigid bodies. The contact satisfies the constraints in geometry and motion. Engagement and disengagement forces with respect to the travel distance of the moving element can be derived for ambient conditions. The calculated force-travel curve agrees with the measured. Finally, influential factors are discussed and suggestions are made for improvement of related products such as accessory plugs.