My random guess is check fuses and check battery. I didn't read that you tested the battery...the first place you start, imho, for anything electric.
Disconnecting is a good start and measure voltage off and on and report back...it may be you just need a long drive to charge up a very low battery, which might be real low for a long time and because of that, the alternator is getting tired also...start with electrical basics and work up and out from there.
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Mangofy your E46!