Okay, $80 later and a trip to Lowes and I'm now a proud new owner of a DC inductive amp meter (the cheaper units only measured AC).
I'm seeing similar behavior at both the battery and alternator.
https://drive.google.com/file/d/1A5S...w?usp=drivesdk
I ran the lights for a couple minutes to drop the battery voltage first. Amperage runs high and steady until the battery comes back up to ~14.5V, then starts to wiggle (the meter doesn't show this as clearly as the amp gauge). I am seeing about 55A @ 3000 rpm. After the battery charged, I dropped to about 1500 rpm where the meter in the video reads ~40A. This mostly held steady on the dash gauge, though I expect it would start bouncing again if I waited long enough. Didn't want to fry anything though.
So, if I have a 60A alternator, is this expected behavior? Or maybe I have a 100A alt w/ 40A load?
Patrick, above you suggested I should not expect to see more than 25A and your math has me scared a bit. I haven't yet seen any evidence of shorting or smoking.
About a year and a half ago, I did have a short under the dash where some previous owner rewired the amp connection through a lower spec connector which had melted. Bob from ERA sent me a new fat black connector to use in its stead and that's been working well since. I'll have to get a scope under there and see if anything strange is going on.