The Elite series 400 amp alternator offers great amperage output and durability at a great price. 6 phase technology, combined with massive twin rectifier assemblies and 12 huge diodes make these alternators totally durable for daily use. These impressive alternators produce 220+ at engine idle RPM and 400+ amps at cruising speeds HOT RATED. Like most high output alternators, this unit comes with a smaller diameter pulley, and will require a 1/2 inch to one inch shorter than stock length belt for proper belt tension in most applications. Installation Notes: This unit may require an additional rectangle to oval adapter harness if the vehicle was originally equipped with the CS144 Heavy duty charging option from the factory. (this is not common) This unit is a direct plug in for any truck originally equipped with the more common oval shaped 4 pin plug as shown.