a method for testing an inverter drive logic switching pattern signal combines six pulse width modulated switching signal pairs into six intermediate signals and further combines these six intermediate signals to produce three composite signals . the three composite signals are used to produce a test signal which is monitored to detect a failure in at least one of the pulse width modulated switching signals . individual pairs of the intermediate signals can be further combined to produce three additional test signals which are used to detect a failure in a particular one of the pulse width modulated signals . these three additional test signals can be further combined to produce a fifth test signal which can be analyzed to detect an abnormal polarity in the pulse width modulated switching signals . both the above test method and circuits which perform that method are disclosed .