Battery light remains on even when car is off.

I have a 1994 Nissan Sentra (100K miles) when I went to get into it today I noticed teh battery light was on eventhough the keys were in my hand. The car runs well except the last few months the battery and emergency brakes flicker and occassionally make a clicking noise while driving. I think the car would start with a jump, but I want to fix this before I fry another battery.