Battery and brake light comming on even after major repairs?

About a month ago, the battery and brake light came on on my 2000 Mitsubishi Galant. The lights would sometimes stay on, sometimes flicker. A couple of weeks ago, I woke up and the car wouldn't start. The battery would go completely dead over night. I had it tested at several different locations who said the battery, starter and alternator were good. No one seemed to find, or care about the reason the battery was going dead. Everyone still said it was most likely the alternator. So as a temporary fix, I had to disconnect my battery every night. On the 13th- My car completely died. The battery went dead, wouldn't start and even the safety lights didn't come on. I had it towed.
Friday, my mechanic had to replace the battery, the alternator, and several wires that he said had been fried. Everything seemed Ok. Monday morning- Car started, but the battery and brake lights still come on. They slowly fade in and out and never for very long and doesn't happen very often. Anyone have any idea whats going on? Could it all happen over again?