This study is carried out to develop an interactive multimedia learning aid that increases students' competency in practicing electrical motor installation. Students of Public Vocational High School in Langkat, Indonesia involve in this study. The Research and Development (R&D) methodology by Borg and Gall (1998) is adapted in this study, in which the steps include understanding the problem, gathering information, design and development, validation, product improvement, product testing, product revision, installation, design improvement, and product distribution. In terms of pedagogy, ASSURE learning model (that consists of Analyze, State Objective, Select Methods, Utilize, Requirement, and Evaluate) is incorporated in the product. When data were tested, the results prove that generally, respondents believe that the developed learning aid is highly qualified to be used. More ever, all parties highly believe that the developed learning aid is able to increase the students' competency in electrical motor installation.