All fuses in the fuse box are new. I've been suspecting the PBCU. It doesn't light up at night like the rest of the dash buttons, so it may not be working but I don't want to buy one as replacement when the one I currently have still works and the problem is something else. I already did that before... with the blower motor. Can you give me a better description of the location of the resistor pack?

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver