Night light setting fails to dim surface light (WITH UPDATE on 9/3/20)

My Adora over-the-range microwave oven has a surface light with a bright setting (push the switch once to turn on), a (dimmer) night light setting (push the switch again) and an off setting (push the switch a third time). A couple of weeks ago, the night light setting stopped working. By this I mean that when the surface light is off, you press the switch and it comes on bright like it should. When the switch is pressed again, the light remains bright (no night light) and pressing it a third time turns it off (like it should). Since the lights work (on the bright setting), I assume that the light bulbs and wiring are intact. I actually replaced the switch with a new one purchased from GE Appliances but the problem persists. Any ideas?

Update: Since the surface light’s two bulbs (the lights that illuminates the range top beneath the microwave oven) are working, I must presume that the wiring and light bulbs are OK. Since I have replaced the switch that controls the surface light (as well as controlling the timer and vent fan) and the problem persists, it seems that the fault did not lie in the switch. Unless I’m missing something, I can only guess that the fault lies with the MICROWAVE CONTROL BOARD (WB56X20629) which GE wants $233.50 for and is shown as currently out of stock anyway. I’m beginning to doubt that it’s worth fixing since I installed it in Nov., 2013, and my previous GE microwave’s magnetron croaked after ten years. However, it seems as if the price of these microwave ovens has risen sharply in the last seven years.

A separate question might be, “ My microwave oven is externally vented. Should I need to replace this oven, can I rely on the external vent location on the back of any new microwave oven of the same size (of any brand) being in a standard location that will line up when installed in the same place over my range?”

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