Hope you and Sabine are well, and enjoying sailing once more.
I agree entirely with your description of the Danfoss-E51385 interface.
To make it maybe a little clearer, in our 24V boat the F pin is driven to +12V to enable the pump. Otherwise it floats (is disconnected) electrically. When it is driven to 12V, then the voltage between the + pin and the F pin is 24-12 = 12V. This is what triggers either the 51385 box or Bill's 12V relay.
As you say, all of this is unrelated to the pump longevity problem.