On the way home from a cruise to the lake, it was getting dark, so naturally I turned on the lights. After awhile I noticed the lights seemed to be almost pulsating. They'd get really bright, then dim down, and do that.

I looked at the battery guage and it was jumping from the middle (13) to the extremely high end (18) and back again.

I replaced the alternator not too long ago (a year?).

 

Is the belt still tight? Very tight!

 

Where did you get the alternator? It might be a junker. Those are the symptoms of a bad alternator/voltage regulator.

 

Belt's still tight. I got the alternator at a Full Service. I could drive the car there for them to check it, but don't want to drive it in the dark because of the lights. The next day I can take it is Tuesday.

Could it be a battery? I didn't think so, but hell, ya' never know.