My red wagon is showing some interesting charging idiosyncrasies. Sometimes, it will act normally and others the voltmeter will bounce a little, then climb sharply depending on RPM. I am replacing the alt today with a known good one, but was wondering if there was anything else I should consider as the culprit to the problem?

define overcharging!

 

if you mean 18+ a wire is disconnected on the back of the alternator

Not quite that high, but it wasn't far off. Swapped the outboard alt for the inboard and deleted the AC at the same time. New alt seems to be functioning just fine.

Usually overcharging is due to a faulty voltage regulator. I had one so bad that did that so i just turned on every single thing i could think of to bring the voltage down until i got to the JY and pulled a good alt.

My alt was bucking out 18v for two short drives, thank god I noticed. The battery was swollen and started to spray acid!

^^^ holy crap