'57 not charging battery

[Denver T-Bird]

I am having trouble getting the battery to charge. I took the generator and voltage regulator to a shop to be tested. The generator was good the regulator tested bad. Replaced the regulator. I tried to polarize the generator by touching the field wire to the battery wire for about 2 seconds (per instructions in the shop manual). When the car is not running, I measured the voltage across the battery at 13 Volts, after starting the engine the voltage drops to 12.7. If I remove the positive cable from the battery when the engine is running it dies. Any suggestions? Thank you for the help.

[paul2748]

Did you check the voltage across the battery at idle? At idle, generators do not put out much over 12 V. Run the engine up to 1500-2000 and check it them. You should get between 13.7 to 14.5

[Denver T-Bird]

The engine was running about 1800 RPMs and only got 12.7V.

[voltron]

Do you have a ground wire between the generator and voltage regulator?