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For years I have had a battery drain never really found so I just used the disconnect switch. Recently I changed starters to a high torque Delco and decided to attack the grounds. I built ground cables for the battery negative to the frame, for the starter to the frame and added one on the drivers side from the frame to the trans bell housing. I used 00 gauge welding cable and solid brass terminal ends well soldered, and ground off all paint on the frame connections. This was instead of the standard over the counter battery cable grounds. Low and behold since then the battery stays virtually charged with no drain and starts fantastic.
This may not be a cure for all but the relationship of weak grounds to the frame or maybe not enough tied back to negative on the battery sure made the difference here.
Having good grounds is always a good thing. But better grounding shouldn't correct a current drain. I don't know how long you've had the battery disconnect on there, but I would be quite a while. And, in that time, I bet you've made some changes to the car...some in the electrical system (or electrical components).
It's more likely that one of those interim repairs corrected the drain and you are just finding out that you no longer have it.