Classic/Antique Car Repair: Battery drain, 67 firebird, auto parts store

Question
Grandson has 67 Firebird w/ 400 engine.  the battery will not hold charge.  previously someone put a battery disconnect in the negative cable.  I removed it but still have problem. Looking for suggestions as to what to look for.  Have checked lights etc.  have not pulled fuses to isolate.

Thanks Dave

Answer
The first thing to do is to have the battery load tested to be sure that it can hold a charge. Most auto parts store will do that for you. I have seen brand new batteries right off the shelf defective and not hold a charge. Then if the battery passes a load test look for a drain in the system. over the years I have found everything from a trunk light switch sticking to after market radios wired wrong. Once the battery passes a load test and the problem still exists, let me know and we will go from there.
Brad