I recently purchased a 1967 Impala SS. The battery has been draining when sitting for an extended period. I have chacked the voltage on the battery at night and it was 12.5V. By the morning it is down to 9.0V. I have gone through all of the fuses and none have been drawing from the battery. I did however find that the voltage regulator was drawing from the battery. With the voltage regulator disconnected the battery did not drain. I have replaced the regulator, but it is still draining the battery. I have not found a short yet. Any suggestions?
Remove all the fuses and if the battery stays charged, then put one fuse at the time. This way you will isolate the problematic circuit. If the battery drains with all the fuses out, then you know that the problem is between the battery and fuse box.
I had a similar issue with my voltage regulator. Except I had it on a battery maintainer and could hear the regulator hum. Took more than one regulator to get one that worked right (I think it was the 4th one). For some reason there seem to be a lot of bad ones for sale out there.
There are six diodes in the rectifying bridge. If any one blows the alternator will still charge but you have a potential to drain the battery as the one way electrical valve that is the function of a diode is now open to allow current to flow the wrong way.