If you use the "search" function, you will find a number of threads discussing how to "decode" the serial numbers. I don't know how well that system works for the Taiwan Schwinns. From your description, the bike sounds as if it is from the late '80's.

I bought a Taiwan Schwinn three speed for a friend. It was about ten pounds lighter than similar models that were made in Chicago, with a better frame, and good quality rims, hubs, and components. There are a lot of these fifteen, twenty, and twenty-five year old Schwinn's still on the road, riding as good as new. A much better ride than the stuff being sold at Wal-Mart.