voltage gage
 

I have a 95' Park Ave. and the battery indicator light comes on sometimes then goes off at random. It has been doing this for about a year and when we had it in the shop a year ago the mechanic said it was a short in the gage cluster somewhere because he laid a tool on the dash and the light went off. That has not really been a problem but lately the needle has been dropping below 10 volts so I put a new alternator on and most of the time the needle is at 14 volts but it has droped below 10 at various times again. I figured if I replaced the alt., the voltage regulator is in the alt. so it would fix the problem. Any ideas what else could be causing this?

Suspect there is a poor connection somewhere. Start with all the ground connections from the battery to all the grounds for the sheet metal including under the dash, if you can get to them. These can be a stinker to find and you or your mechanic might get lucky and hit it right away.

When the dash gauge needle drops, have you ever compared the readings with those of an actual meter on the battery?
Just wanting to confirm that the voltage in the system is actually dropping, and not just the gauge and light misrepresenting themselves.

If it's actually reading low, then it's either an alternator/regulator (like you were thinking when you replaced your old one), a bad connection, a bad wire, a bad battery, a partially blown fuse (unusual, but happens) or something else in the circuits that control all that.

If it's just the gauge and light that are reading low, then what your mechanic said makes sense. Either there's a bad connection at the dash panel, a broken trace in the PC layer (if the Buick uses that kind of cluster), or most likely it seems to me, a burned out resistor or two.

Again, not sure about your particular car, but most that I've worked on had either a resistor module, a special circuit on the PC layer, or literally resistor(s) soldered into the circuit on the cluster itself.
I don't pretend to know how all that works, but I know that they can cause at least the lights to misbehave.

Good luck.

Paul