A retrofit diverter switch which has a mechanical and electrical interface that is compatible with the existing designs is provided. The diverter switch may include a vacuum switch. The feature where the mechanical and electrical interface is compatible enables a retrofit from traditional On Load Tap Changers to a vacuum based on Load Tap Changers. The diverter switch may be retrofitted into existing tap changer housings. Retrofitting from traditional to vacuum based, traditional to vacuum based and up rating, and vacuum up rating may be possible. Also, the diverter switch may include modular components that allow for easy customization of the diverter switch for different applications.