A secondary drive device of a mobile working appliance with an electronic control unit for actuating a power take-off shaft clutch arranged between a transmission and a power take-off shaft is disclosed. According to the disclosure, the control unit is designed with a flange-mounting function unit which, when activated, executes a rotary position correction of the power take-off shaft with respect to the drive shaft. Furthermore, a method for coupling and/or uncoupling a working machine to/from the secondary drive device of a mobile working appliance as an energy source is proposed. The method includes the steps of leading a drive shaft of the working machine up to the end spline shaft profile of a power take-off shaft of the secondary drive device, checking the relative rotary position of the power take-off shaft with respect to the drive shaft of the working machine, and selectively triggering a flange-mounting function of the secondary drive device as a function of the result of the check of the relative position for the electronically controlled rotary position correction of the power take-off shaft with respect to the drive shaft.