As I recall, there are two different relays, four pin and five pin. If you get all five pin relays, they will work in any slot, four pin or five pin. A four pin re;lay won't work in a five pin relay slot. So it is better to only buy five pin relays. They will work in any of the five relay locations. The extra pin on them simply goes unused when you put a five pin relay into a four pin relay slot.