The redneck in me would be inclined to introduce a switch on that circuit before the fuse, to shut off the power to that circuit when it's not in use...locate it below the dash, or in the console.

Don't laugh...you wouldn't need to spend hours searching for the issue, and have a simple way to shut it off and save your battery.

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1987 560SL
85,000 miles

I though of that but the circuit is back up memory to lots of stuff that needs to be relearned and reset every time it looses power. It also powers the keyless entry.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

Don't laugh at this, when I was a young farm boy I learned all manner of "Farm Fixes" and still use some to this day .

Sadly this one is trickier , I wonder of getting behind the fuse box and separating the wires / circuits is possible .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better