Lean Manufacturing (LM) is one of the most popular production systems used by companies across various industries worldwide. LM was developed based on the Toyota Production System and includes a set of methods and tools whose application allows for the improvement of production processes by eliminating existing waste. Identifying waste in the process and subsequently analyzing it is the foundation for undertaking improvement actions. The work aims to present an analysis of the assembly process in an electrical engineering company in Poland in terms of identifying losses, through observation and measurement of the time of activities performed by three operators on a selected production line, due to the problem of achieving the required level of the efficiency indicator. The analysis was carried out using the “Red and Green” tool, which reflects value-adding and non-value-adding activities in the process, by the LM concept. The obtained results allowed for assessing the assembly process in terms of losses occurring for each operator, which was the basis for taking improvement actions. Solutions were proposed for those activities whose share in the total time did not exceed 7%. Then, the potential effects of the changes were estimated in the form of the possibility of increasing the production volume on the assembly line for the component with the highest demand in 2024. It was estimated that implementing all proposed improvements would allow for savings of 775,741 s per year, translating into an increase in the volume of components produced by 5,614 pieces per year.