Need to know where to start looking for electrical issue on 1996 Buick LeSabre.

Until actual testing is performed - can’t possibly determine ‘what’ the failure is! Simply replacing the alternator doesn’t mean it is performing as it should.

Thanks, I've done that and all's good there. Have new alternator. What would cause complete power outage one moment then later on allow power to come back on? Battery /Alternator are good. Seems to occer after running awhile.

I’m thinking there are two *positive battery cables* - I’ve seen corrosion build up between these two cables and cause the symptoms you’re describing. That can cause this to happen ‘intermittently’ as well. Clean battery cables until they shine - then clean em again!