Well at least remove and inspect possible worn alternator brushes from the list of culprits, as Alistair has suggested.
 It's been a long time, but I remember using one those sideways screwdrivers (slotted) to achieve this determination.  

Yes...fiddle around with it a bit.  Jiggle things.  I was amazed when a long time ago I removed the carbon brushes in my alternator:  man...they had shrunk down to almost nothing.  Just the way it goes.  Things wear out.

Rich
San Diego

    On Tuesday, April 7, 2020, 7:34:48 PM PDT, Alistair Bell <albell@shaw.ca> wrote:  
 
 I’m cooking, I mean really, so quick....

Alternator voltage reg... brushes worn out.

My first guess

Alistair 

> On Apr 7, 2020, at 7:31 PM, Gregg Carlen <gricha@verizon.net> wrote:
> 
> Hi folks,
> 
> I’m cruising along this evening about 60mph on the road and my battery light comes on. I slowed and it went out. 
> 
> After some trial and error, I figured out everything is okay if I keep the rpms under 3200. If I go over that, the battery light comes on, and very soon the dashboard lights dim and headlights dim. I let off the gas to get under 3200 rpm and the battery idiot light goes out and everything brightens up again.
> 
> Could my voltage regulator be going bad? Alternator? Something else I should look at?
> 
> I’m still traveling, so hopefully o can nurse it the rest of the way home.
> 
> FYI; 1990, almost everything stock on a 2.1l. Don’t have access to my records right now, but o don’t think the alternator is more than 5-10 years old. The belt was just recently replaced. Had about 0.5 - 1” flex in it. Could it be too tight?
> 
> Thanks in advance for any advice!
> 
> Gregg
> 90 Westy