What is Pulse Width Modulation (PWM)? Pulse Width Modulation (PWM) wiring systems, sometimes called "Multiplex," are systems that vary the signal intensity over one wire to initiate more than one lighting function - like running or stop lights. There are two types of PWM systems, ST and STT. ST systems have one wire that contains both stop and tail functions, and a separate wire on each side that contains the turn signal functions. STT systems have one wire that contains stop, tail, and turn functions. Please note this product does not ship to Pennsylvania. This item is compatible with the following vehicles: Audi * 2009 - 2009 Audi Q5 CUV Mercedes-Benz * 2010 - 2010 Mercedes-Benz E350 Sedan Volkswagen * 2010 - 2010 Volkswagen Golf Hatchback * 2010 - 2010 Volkswagen GTI Hatchback PWM CONVERTER MODULES * For use with Pulse Width Modulation Systems (PWM) * Now with "New" Surface Mount Technology (SMT) * Virtually Eliminates Draw on the Vehicles Taillight Circuit * Maximize Trailer Light Brightness