Classic/Antique Car Repair: Battery Discharging, load test, charging system

Question
Car is 1955 Thunderbird.  Battery does not charge while running and is dead overnight.  I have changed the solenoid, voltage regulator and put in a new battery.  How can I find out what is discharging it overnight.  Even when it runs, the gauge shows not charging.   Is it a ground wire somewhere?  Thank you

Answer
My thinking leads me that you need to do a charging system test. That is to check the output of the generator, the setting and operation of the regulator, and a load test of the battery. Once these test are done and they check ok then we suspect a draw in the car that is running the battery dead. The clue here is that you are not showing any charge when the engine is running.
Brad