NOVELTY - Potentials tapped off from the series circuit are connected in arbitrary succession to a switching array forming a measurement position selection switch (SM). The tapped potentials in the series circuit are first measured automatically by switch (SM) operation. The measurements are used to control the switch (SM) such that the measurement transducer (MW) is connected to potentials (P) corresponding with differences in the contributions of individual electrical components in the series circuit.    USE - To detect potential differences in e.g. fuel cell stacks, batteries or series electrolysis circuits.    ADVANTAGE - Fuel cell stacks, e.g. those used to power electric vehicles, contain increasingly large numbers of cells in series, in order to reach high output voltages. Testing to find failed cells becomes a problem. The cells may give little or no output, and it is even possible that the potential will reverse. The new method considerably simplifies the wiring required for testing any type of series circuitry using a switching array or multiplexer. Cells are tested in pairs, only the potential difference being measured and amplified (MV). Use of switching logic enables rapid convergence onto the cell(s) responsible for reduced voltage output.    DETAILED DESCRIPTION - Automatic measurement is commenced by an external command, especially by pressing a button. The automatic determination is made to detect variation of the sign of differential resistances in the series circuit. During automatic determination, the tapped potentials are compared in pairs, to determine the sign of the potential (P) differences. Automatic determinations are made in accordance with a sorting algorithm. Tappings are connected to the switch (SM) in completely arbitrary succession. Potential tappings are connected to the switch in two groups, followed by connection in arbitrary succession, to the switch (SM). AN INDEPENDENT CLAIM IS INCLUDED FOR corresponding equipment.    DESCRIPTION OF DRAWING(S) - The drawing shows a simplified schematic circuit diagram of the switching arrangement.    analog to digital converter (ADC)    measurement amplifier (MV)    measurement transducer (MW)    potentials (P1-P4)    measurement position selection switch (SM)