Functional mock-up units (FMUs) are three-dimensional test boards in which a number of vehicle components can be integrated in their original state. This is the perfect way to subject, in particular, the cable harness and ECUs to complex networking and function tests – in conjunction with real sensors, actuators and other subsystems. A suitable mechanical setup means all essential parts of the test setup are easy to access. Original parts can easily be substituted by spare parts or simulations at any time – and vice versa. FMUs thus enable high-quality flexible tests for series validation long before the test is possible within real vehicle bodywork.