Your 12V pump is looking for about 4A supply at 12V according to its specs. The system is designed to operate with a pump supply current of 1- 1.2A at 12V. I suspect you have damaged your 51385 module.
Did you ever connect a different 12V pump from the specified pump by Frigidaire ? Maybe your 51385 is also fried.
I agree with your description.
I suggest to buy the correct pump, and with a 'working' 51385 (operating at 12V) everything should be fine.
Using the correct 24V pump, the pump is safe under fault conditions, so you won't damage the pump if the voltage regulation on the 51385 fails. The 24V pump operates on a lighter duty than a 12V pump operating at full tilt. This extends its life and makes it quieter.
Just need to be careful with specs about the pumps. Veco rebadge the Flojet 24V pump as a '12V pump' for continuous duty at half the flow rate.
This can be very confusing when discussing the pump, or trying to replace it with a different one.
Fun and games indeed!
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