The early style OEM 31506-79B starter relay is found on most 1980-1992 Harley-Davidson models. The late type OEM 31504-91A starter relay is in fact the same but has a built-in diode and was introduced in 1991 on Touring and FXRP Police models, and than used from 1992-2008 all Big Twin and 1992-2004 Sportsters. The early style is available as a stock replacement relay that is an equivalent to the OEM part, as well as an improved updated, skirted version, that is really weather proof with a skirt that protects the connector block. Late style starter relays can also be used to replace the early style.