Battery voltage drop

Yes you need the second field connector connected to something. If you are using the old style regulator then that tab needs to be grounded. If you are using a new electronic voltage regulator you need to have the blue wire extended from the ballast resistor and connected to the second tab. The regulator cannot sense the battery voltage unless the alternator is connected correctly. If there is no voltage sensing happening there will be no charging even though all components are good.