2002 4cyc Sonata sat with dead battery for a month. I charged the battery and outside lights and dash lights began blinking constantly. When I turned on headlights all this stopped. As soon as I turned off headlights all the blinking started again.This happened with the car off or running. I let the car sit with the battery disconnected while I ate dinner and then connected the battery and started it again. The blinking started again even with the car turned off but stopped blinking after about 30 seconds. This continues still. Any suggestions would be appreciated. Thanks