Not sure I got your full question. The simple way is to turn the AC on with the car warm. Depending on the model year and package it will turn on immediately or there might be a short delay, but it is short. My guess is the later cars use more of the other two sensors that watch the AC system.Without access to INPA is there a way to test the aux fan direct outside of the care. Example checking a spare used?
Don't think we ever got to testing the supply control voltage to emulate what controls the speed. You need an oscilloscope for that, I am sure this was on 68's list but don't remember him doing it. My tests with a 9v battery did not yield expected results. So as far as I know we have no idea if a short pulse makes the fan run slower or faster. A near 5v constant signal might make it run slow, or a slow pulse of 5v might do that.
Really all you can do is run the AC and see if it works. We also have no idea what the car uses to decide what speed to run the fan at, there are two pressure sensors on the AC, then there is the lower coolant output temp sensor, and last road speed that come into play. If you are having issues with the AC, or road speed sensors, and don't have the cold weather package or you car is later than the official change to the 3 wire system, your results may vary.
That said turning on the AC with the car parked in the drive warm has been a reliable way to find many a bad fan, before they start the burning up process because it seems pretty clear the lower speeds go first even though full speed may last for a longer time before it fails.
My suspicion is the damage to the fuse and wiring happens when only the full speed is working, but that is just a guess from where the damage has been found on the board posts.