Charging system fluctuates voltage???
 

88 GXL, only aftermarket item is CD deck.

The alternator has been charging at 11V or so, sometimes lower. with headlights, blower motor, and CD deck running. With only cd deck running it will jump to 12.5 or so. With no extra loads it will fluctuate b/t 12V-and on a good day 13V, just depends on the day. I have replaced the alternator 3 times (warranty). each time with a new battery (warranty). And since the voltage regulator (my first thought) is internal with the alternator, I dont know where else to look. I thought about checking grounds, but this didnt start till about a year or so ago. Never had any problems before that. Any help on what to test is apprciated.

-Zach

mine does that when i dont tighten the battery cables enough. could be that. do you use dielectric grease when you put the stuff together?

Have you checked for voltage drops in the wires? High resistance will not only create a voltage drop where it won't charge right but will create heat and that is bad. It's easy to check with a multimeter.