CW, from what I remember from Lenny Dean many years ago, the relay was used to ring the telephone bell when there was an incoming call. They were no longer made after the mid-sixties as telephones went solid state. That's about the time Lionel no longer used mechanical whistles and horns.
We have all heard the stories about Lionel and Ives reversing units, but never about the DC relay. Probably because they came from an outside supplier.
