Abstract: An arrangement for detecting faults in automatic test systems of the type wherein test points in a unit under test are connected to test instruments by the programmed closure of electromechanical relay contacts. Respective contacts of the relays are connected to each other and, during periods intermediate of the closure of the relays, a detector circuit is coupled to the interconnected relay contacts. The detector circuit compares a voltage or resistance present on the interconnected relay contacts to a threshold. In one embodiment, if a difference between a signal on the interconnected relay contacts and the threshold persists for a predetermined period, an interrupt signal is generated which prevents further closures of the relays. In this manner, catastrophic failures of the unit under test and the test instruments are prevented.