The Custom Fit Multi-Platform Performance Stereo Replacement Interface combines applications from 11 interfaces into one. S3-SR1 covers over 125 applications in nearly 40 million vehicles. It reduce install time with built-in plug with no programming necessary and provides 12v ACC output with RAP and all navigation outputs. An interface is a small computer system that allows your new head unit to properly communicate with your vehicle's computer system. If you install a new aftermarket radio without using an interface, you will lose many of the standard security features of the vehicle. This is due to vehicle manufactures running part of the vehicle's computer system through the OEM radio. Functions lost include, but not limited to, are warning chimes (keys left in ignition, lights left on, low fuel etc.), security and alarm systems, +12V accessory and more. If the +12V accessory is lost, your radio will not turn on/off automatically and will be a manual process.