Factory ammeter

but every time I looked it was max out at +40 the late
There's the cause.
Sorry if I hadn't directed your attention to this some point in the past.
Also check the fusible link and the battery acid.
For future reference, the system will tolerate 20 - 30 amps for brief periods of time. Brief as in a minutes, but not 15 or 20 minutes. Pegging either direction is into danger territory, shut it off.

Charging Battery with Alternator - Warning