While I don’t profess to be an expert in automotive electrical issues, I just recently had to deal with a similar issue on one of my larger CASE Loaders that was 'draining' while parked. The first thing I might suggest is determining if there is really a drain, or if the drain is from lack of use.

If you have access to a quality meter (with a milliamp setting) disconnect the battery at the ground, then bridge the meter between the ground post and the ground cable. If there is a drain (with meter set to milliamps), it will show up. If you find a small drain, start removing the fuses one at a time and check for the drain. This will at least determine if there is a drain, and on which circuit.

On my Loader, I finally narrowed it down to a ‘failing’ Motorola radio that was pulling power when off. The drain was 4 milliamps, and without a quality meter I would never have found it.

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82 380SL 41K miles sold, 98 SL500 44K miles, 13 C300 4Matic, 14 CLA-250 4Matic