Is it normal on our cars to have the battery light flicker on and off once in a while. It's been doing that and today it stayed on for like 15 seconds while driving at night with radio and lights on. Never done that before just wld flicker. I have checked my volts and running they are constantly over 14 volts. My battery is good and my connections are very clean. I have read of other mustangs with this problems so is this normal???