I don't know what ignition switch you have, but some of them have a terminal that stays hot all the time. When I first put in the aftermarket turn signal on my '51, I connected the signals to this terminal so that I could run the flashers with the ignition off. Bad Idea. I ran the battery down numerous times, because either I left a blinker on, or eventually the peanut light in the signal switch would run the battery down if I didn't drive for a few weeks.
So you may have the accessory wire of the harness connected so it will power you gauges all the time. This will drain your battery. I would change this if I were you.
Also, your new battery might have not had a full charge, or might have been "old" on the shelf. I would check the date code on the battery, and if it is not recently manufactured, I would take it back and ask for a new one.
Kurt
