Abstract: Electronic circuitry is disclosed for interfacing with a plurality of two-position switches to determine if each switch is opened, closed or faulty to some extent. Each switch is connectable in series with a pull-up resistor and between two different voltage values. The switch provides an output voltage at the connection of one terminal of the switch with the pull-up resistor. This switch voltage is presented to both an inverting input of a first comparator and a non-inverting input of a second comparator. The non-inverting input of the first comparator has a reference voltage of a certain value applied thereto, while the inverting input of the second comparator has a reference voltage of a certain value also applied thereto, the reference voltage values being different so as to define a "window" or "dead band" region of voltage. The switch output voltage is compared to the reference voltages on the two comparators. If the switch is closed, the comparator outputs will assume certain states.