So while driving my 99 mustang lately, once up to operating temperature my battery light comes on for about 10-20 seconds, and then goes back off on its own. Has done this during acceleration and during cruise, also today it came on twice, going off both times in 10-20 seconds. Both the battery and alternator have checked out good in testing done by checkers. No changes have been made in the electrical system. My mechanic and I are both stumped. Are you?