Abstract: A window defrosting grid testing apparatus which is automated to test the resistance grid for quality control relative to set automotive standards including the continuity of each line of the grid. In one preferred embodiment, the testing device includes means for automatically clamping the window in position on a support table and engaging a set of three conducting probes in conducting contact with the grid at predetermined locations associated with opposing ends of the grid lines and an intermediate position between the opposing ends. The probe in the intermediate position is mounted for lateral and transverse travel across the grid lines and is operatively connected to a voltage sensitive relay which operates to provide a signal only when the energized grid line engaged by the intermediate probe is non-defective relative to continuity.