Dave , I have to disagree on how to test generator / regulator output.
"B" circuit generator / regulator (original Thunderbird).
You NEVER want to jump battery terminal to field terminal at the regulator with the wires attached to the regulator. This will burn out your voltage regulator field contact system in your regulator.
Testing your generator / regulator for output :
Remove field wire from voltage regulator and with engine running at 1200 to 1500 rpms. Touch the field wire to armature terminal at regulator for a few seconds. If the voltage increases to 14 to 15 volts. The voltage regulator is bad. No change in voltage the generator is bad or wiring issues. This test is unregulated so do not run for more than a few seconds to read your volt meter.
Always check wiring for a good ground (no voltage loss) between regulator and generator , frame , block , battery.
Polarizing your "B" circuit generator :
Engine off. Disconnect the field wire from your regulator and touch / flash to battery terminal on your regulator.