The diagnosis of the failure mode in defective interconnections requires the localization of the failing via before the visualization is performed. The exact localization is challenging when the test array consists of several thousand interconnections and is even more difficult when we have to deal with contacts on active area due to leakage currents into the substrate. This paper shows that Active Voltage Contrast (AVC) and Seebeck Effect Imaging (SEI) are complementary methods to localize defective interconnections in cases where passive Voltage Contrast or other laser scanning techniques fail. It shows that the two physical approaches yield different information. AVC has advantages in lateral resolution and speed as it allows localization and direct cross sectioning in one step. While SEI often overlaps with AVC, it makes resistance mapping of a large area possible and is the method of choice for marginal resistance increases with high sensitivity.