I had a similar problem after upgrading to a zx alternator in a 1976 280Z. The brake warning lamp check relay was draining the battery. I had used the atlanticz instructions and the relay ended up "always hot" (not atlanticz's fault since the instructions were for a different car). With the old mechanical regulator the relay only got power when the motor was running.
If you hear a relay clicking when you reconnect a charged battery, it could be the problem.
I ended up cutting the relay off of the always on power circuit and splicing it in to the fuel pump circuit, which has a connector under the passenger seat, where the brake warning check relay is. The car will run and stop draining the battery if you just unplug it, but the red brake light in your dash won't work anymore.
According to the wiring diagram there is also an EGR solenoid on the same circuit as the brake check relay. My car doesn't have one but yours might.
