pulsating voltmeter, Buick 88 3.8

That sounds about right. When the turn signals blink, there is a small fluctuation in the voltage. However, you ought to have an electrical system check. Specifically, the battery and the alternator. If some of the rectifiers of the alternator have blown open, then you see more of this kind of fluctuating voltage.

---Bob Gross---

My idea is that it's normal.

Unless the "dip" is substantial. how much a voltage swing occurs?

Is the battery charged? Are the lights & other electrical accessories lasting normal length of time? Most gauges are there for entertainment value and tend not to be exactly accurate.