Perko 250 Amp Battery Selector Switch with Alternator Field Disconnect Designed for surface mounting, the Perko Battery Selector Switch has a bright red polycarbonate housing with a large easy-to-turn black knob. The Perko Battery Selector Switch has a number of functions they allow for a quick and easy way to shut down the entire electrical system in an emergency this device also permits battery selection of two or more batteries for specific purposes, including starting engines, running acces