This handy little adapter harness allows you to plug an oval 4 pin late model GM alternator in to a Rectangular CS130 or CS144 vehicle harness. This harness is required in order to install certain high output alternators on GM trucks that originally came with a CS130 or CS144 alternator with a rectangular plug from the factory. This is common on most 1988-1995 GM trucks, as well as some later models equipped with the heavy duty charging option.