Alternator Troubles! 1973 Plymouth duster 318

Hey yall, I've Been slowly working out all the electrical gremlins in my car for the past year, and I have 2 big ones left. but as of right now, id like to figure out why my alternator isn't charging, the main Wire (I don't know the correct names of these Wires) reads a constant voltage from the battery and slightly drops when under load (E.I putting the key in the ON position) but the BLUE and GREEN wires (Field wires?) show no voltage what so ever.

so here's my main question; Where do I start?

I have a brand new alternator in the car now just for preventative maintenance, which I tested in another vehicle and is working fine. and I have good quality wire on hand if I need to run some new ones, but I don't even know where to start when it comes to that.

I really appreciate everyone's time and will be watching this thread religiously, so don't be afraid to throw down some knowledge, I'm only 20 and have a good but limited knowledge when it comes to electrical systems in these A-Bodys, so I really do appreciate anything I can get.


Thanks!
Blaize