a method of installing a belt driven accessory on an internal combustion engine in which consists in an oem dual alternator installation having two oem alternator mounting brackets , each bracket configured to receive an alternator . the accessory is attached to an adapter . the adapter is attached , with the accessory attached thereto , to one of the two alternator mounting brackets , in place of an alternator which might have otherwise been attached to said one bracket ; and a single drive belt is placed in operative position to drive the accessory attached to one oem alternator mounting bracket and an alternator attached to the other oem alternator mounting bracket .