After 7 years of staring into the darkness where the rear fan & side mirror defoggers switches were, I sourced a used hazard/antenna/CDL switch (8401060480) that had the same bulb w/ brown rubber holder. It was a bit of a struggle to remove the back plate of the circuit board, but finally managed to pry it off w/o breaking anything. Now all switches light up as it should

. However, one thing I realized was that one of the bulb I removed works. The conclusion I have come to is these are wired/circuited in series. So make sure you test both bulbs once you remove them to make sure both are not burnt out

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