A switch interface adapter allowing a simple open/close switch to be adapted to a digital and analog diagnostic switch interface includes: at least one coil having a first terminal and a second terminal, wherein the switch is electrically connected to the first terminal or the second terminal, and the at least one coil is activated or deactivated via the switch; a first contact switch comprising a digital line, wherein the at least one coil controls opening and closing of the first contact switch to break and complete the digital line respectively, the digital line is electrically connected to the ECU, and a digital signal is generated from the digital line as a digital input for the ECU; a second contact switch comprising an analog line, wherein the at least one coil controls opening and closing of the second contact switch to break and complete the analog line respectively, the analog line is electrically connected to the ECU, an analog signal is generated from the analog line as an analog input for the ECU, and the digital line comprises a first resistor serially connected to the second contact switch; and a second resistor comprising the analog line, wherein the second resistor is parallel disposed across the first resistor and the second contact switch. The ECU compares the digital input and the analog input to diagnose the switch interface.