Abstract: Method and apparatus for testing D.C. motors, D.C. generators, electromagnetic devices, and the like is disclosed. An electrical circuit produces a current limited, pulsating or otherwise time varying direct current signal which is applied to the device or component under test. The signal induces a return signal in the device or component under test, or in a magnetic sensor placed in proximity to the device or component under test. The return signal is amplified and displayed on an amplifier output display. Novel methods are disclosed which utilize the apparatus to (1) determine and set the neutral plane in a D.C. motor or commutator type generator, (2) locate grounded, shorted, open or crossed coils or bars in an armature of a D.C. motor or a D.C. generator, (3) determine the relative magnetic polarity of the windings of various electromagnetic devices, and (4) detect shorted, grounded, or faulty field windings of various electromagnetic devices, including field coil windings in D.C. motors and generators.