Your bike is probably a Japanese-made Schwinn assembled in March 1985.
The headbadge number can be decoded as such: 74th day (March 15) of year ending in 5. So March 15 1985.
There were various serial number formats over the years. Your format looks like the format S(month letter)(year number)(frame number) which was used for Japanese-made bikes. So SC502550 would be the 2550th bike assembled in March 1985 in Japan. That's consistent with your headbadge number.
I believe Panasonic was the contractor building these at this time but not 100% sure. Someone with more Schwinn knowledge can correct me if I'm wrong. During the 80s I know Giant was also building for Schwinn but that would have been made in Taiwan so probably a different serial number.
Last edited by TenGrainBread; 05-20-19 at 06:59 AM.