I have the same problem with the 98 corolla LE. The light on/off when or when not the seat belt is off/on. I have unplugged the switch in the seat belt retractor area and the light remains on and I plug it in and it is not relible. Do you suppose it could be not a good connection??
Also when my DRL are on the instrument panel lights are on and when I monkeyed with the seat belt switch I noticed that the instrument panel lights were off when the DRL was on.