Regarding the "master switch," is that the driver's door window control console? I know that so much runs through that, that calling it a master switch would make sense. In fact, when I installed my (turned out to be) faulty DLA, I accidentally dropped that window switch cluster on the ground when something suddenly required me to have an extra hand that I did not have. When I had weird behavior following the install there, I was not sure if it was the DLA or that switch cluster. Since it mostly worked, I did not worry about it until recently.

Unlike the DLA, that window switch cluster can be removed all by itself using nothing but your fingernails. It might be useful to see how the system responds now, when things are working fine, with that removed. Then you'll better know how to interpret the change when the problem is present.

Actually finding the failed part can be difficult. So when I was doing this last month, I first took the window switch cluster apart (having read many reports on here), inspected, hoping to find clearly visually failed solder joints. Only found one suspect, fixed it with no change.

Next easiest thing, while putting off serious fault isolation debugging, was to buy a replacement switch on eBay, which I did, with no improvement. It actually worked worse, which was puzzling. Then with the good DLA reinstalled, both eBay and my original window switch clusters worked fine.

So at that point, I spent a couple of hours doing serious, careful, experimental-mode testing with the INPA and Foxwell. Isolated the fault to the DLA, mechanically repaired my old one (plastic bracket had cracked and initial quick repair attempt did not hold), and swapped it in for the win.

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2001 X5 3.0i, 203k miles, AT, owned since 2014