[DanEC]

I had a lot of related issues with my ERA when I was getting it up and running. I suspect that basically the red light circuit isn't exciting the voltage regulator into "regulating" and since the alternator isn't hearing of a demand from the VR, it's not charging above the default 12V.

It's a confounding problem to resolve. Even when my charging light bulb was burning I didn't have enough resistance to excite the VR and ERA had to rig up a resistor to work in parallel with the bulb to create enough circuit resistance. But since yours was working before something has changed. I understand that bench checks of alternators is sort of an iffy thing. They may produce 12 V but will they spool up to the 13.5 to 14 V as demand is put on the charging system? You may have to try another alternator but most dealers are hesitant to take back electrical parts that have been installed.