ESR310 was designed as a high quality replacement regulator for the Yamaha XS750, XS850 triples and the XS1100 big four cylinders from the late 70's to early '80s. We installed our modern field control circuitry into a dedicated heat sink and outfitted ESR310 with quality wiring and connectors that plug right into the stock wiring harness. This ESR310 will give you a much more stable battery charging voltage across the RPM range and the modern electronics internally run much cooler than the OEM units. ESR310 comes with a full one year warranty.