We apply pressure-modulated conductance microscopy to metal/molecule/metal switches. Apart from pressure-induced conductance peaks that indicate nanoscale conducting pathways, we also observe dips and oscillations for devices with conductance between 1 and 2 conductance quantum. The conductance oscillations arise from interfering electron waves along one or two quantum conductance channels between two partially transmitting electrode surfaces at room temperature, underscoring these devices' potential as coherent, atomic-scale switches.