The invention relates to a measuring apparatus used for testing the connections between at least two subassemblies (3, 4, 5), comprising a test system (1) for generating a test signal available on an output of the test system and for evaluating an analysis signal produced by a subassembly (3, 4, 5) from the test signal and received on an input of the test system. The test system (1) is also provided for applying a switch control signal to a controller (10, 11, 12) included in a subassembly (3, 4, 5). A subassembly (3, 4, 5) includes a switching circuit (7, 8, 9) controlled by the assigned controller (10, 11, 12), which switching circuit is provided for directing a test signal or an intermediate signal formed from this test signal to a test input of a subassembly and for receiving at least a further intermediate signal from a test output of a subassembly. A switching circuit (7, 8, 9) in a first position is provided for coupling the test input of the subassembly to the output of the test system and for coupling the test output of the subassembly to an auxiliary line (BR), and in a second position of the switching circuit, for coupling the test input of the subassembly to an auxiliary line (BR) and for coupling the test output of the subassembly to the input of the test system or to a further auxiliary line (BR).