Jumpy volt gauge

Is this just at an idle? I had one on my 77 W200, did the same thing. Going down the road , it smoothed out. I don't think the engine turns enough rpms at idle to "excite" the alternator. Someone smarter than me can give you a better explanation.

Actually, I hadn't noticed whether this is only at idle. That IS when I looked down and noticed that it was jumping around a lot. I'll check it at cruising speeds tomorrow. Thank you.

New doesn't mean a whole heck of a lot today. Could very well be a bad regulator.
Could be a poor ground connection(s) too.
The regulator must be grounded at it mounting. The ground wires to engine and chassis must be clean and tight.

I know new doesn't hold much water now-a-days(this is alt #2, first was bad) but was kinda checking on here for other possibilities. As for connections, that is why I stated all new connections(with new wire and connector ends with bare metal points of contact. Thank you.