To verify the field lead is working ok disconnect the connector on the back side of the alternator. Then turn the key to the RUN position and check the battery warning light on the dash, it should be turned off. Then reconnect the alternator plug and verify the battery warning light is on. If that checks out then the alternator will have power to the exciter and should generate power. Check the voltage on the main output stud of the alternator and see if you have more than 13 volts there while the engine is running at about 1,200 RPM. If that is ok then measure the voltage between that point and the positive battery post. If there is more than .3 volts difference then there is a problem with the connection. Check the fuse.