On an related topic, sometimes when doing a brake job, the emergency brake gets bumped. Usually only one click, and the Brake light comes on. Make sure the emergency brake is all the way up, and the switch located at the top of the pedal is no longer depressed. If it is, with the emergency brake all the way up, loosen the switch and move it away from the pedal until the light goes off. Then tighten it. Your issue with the light may, just may, have little to do with the work you performed (with a little luck).
The brake system should be opened and flushed as rust has contaminated the system. Its possible that the rust has accumulated in the the lines or more than likely in the proportioning valve causing the light to stay on.