If it was the radio, fan motors, coil etc would be fried every few weeks.
I googled the alternator you listed and it is a 1 field wire alternator.
This is the photo they show on the website ( red terminal is grounded)
View attachment 1716170879
This is most likely what your alternator looks like..
round back alternator cores are in short supply so rebuilders internally ground one of the field terminals of a square back alt.
The blue is a grounded terminal.
the red arrow shows the CUT OFF terminal end ( your green wire is most likely attached to the stub that remains)
View attachment 1716170877
This is an alternative method of grounding a square back to function on a 1 field wire round back application. Note the connector and green ground wire.
View attachment 1716170878
