Ice Dispenser auger won’t stop dumping ice into chute

I have a 9 yr old Kenmore side by side fridge (Model #25355699407). The external ice/water dispenser panel leaked for years, eventually bubbling out the exterior paint, and rusting the door. I removed the ice/water dispenser panel to refinish the door, which involved disconnecting the ribbon cable which connects the Dispenser power board to the Dispenser Control board. Now, when I re-connect those with the ribbon cable and plug in the fridge, the ice dispenser auger immediately starts dumping ice into the external chute and won't stop.

I've tried/tested:

1. Replacing the ribbon cable – same result
2. Testing/replacing the micro-switches – same result

My next steps are to replace the Dispenser Power Board or Dispenser Control Board, but as these two parts run around $150 EACH, I'd like to know if anyone has any advice, specifically regarding:

1. How to figure out which of the two boards may have failed
2. If I start with one board, and choose the wrong one, am I at risk of damaging the other?
3. Is there any other part, inside the ice maker itself, which may have failed? I'm a little unclear about how the dispenser controls "talk" to the auger.

At this point, it is actually just about as expensive to buy a whole new door as to replace both circuit boards, which leaves me pretty frustrated.

Additional curious note:
The last time I put everything back together and connected the ribbon cable, with the refrigerator still unplugged (and had been for at least 15 minutes), I saw a flash behind the Dispenser Power Board.