OK, I know this is an old thread, but it will make sense
Going through some 862 and 890 horn relays (cleaning and testing) and I found a letter code. On the topside of the plastic housing, I have a G, C, E & F. They look like months to me. I have one more I need to check
Since these were kinda made in calendar years, it would make sense. C=March, E=May, F=June and G=July. Anyone else see those?