While idling at 800 rpm I have 12.2v at the battery and 11.8v at the blue field on alt. I jumped 12v from the battery directly to the blue field and it continued to charge full steam.
You're making us read between the lines here.
If doing so correctly..
Test 1.
Engine running 800 rpm
12.2 V at Battery
11.8 V at Blue wire on field terminal
ammeter showing 40 amps charge ??????? If so this would indicate a dead battery or equipment wired to the battery.
Test 2.
Engine running 800 rpm
??? V at Battery
??? V at Blue wire on field terminal
Ammeter showing 40 amps charge
I'm guessing this was a test to eliminate possible voltage drops.
It halfway did that.
There still could be drop between the alternator and the main splice.
Better to three test points suggested in my earlier post. That plus the ammeter reading should reveal the issue.