Hello again, before I forget let me say that each time a part is replaced there is the chance of an error... its best not to replace parts before testing and finding them bad.
None of those parts would cause an actual high voltage condition... the problem is in the voltage sensor the company uses most likely 98% chance thats the case.
The 3 amp fuse is related to the 24 volt control circuit... and would normally not cause a 'high voltage' read on the hi/low voltage sensor read out.... those are two different things.
the whip that runs from the side of the house to the unit could have been the problem judging by the water in the protective sheath.. and cuts in the wire insulation
would cause the 3 amp fuse to blow... the cure for that is to buy another length of thermostat wire with the same colors of conductors and replace the thermostat wire you have...BE VERY CAREFUL TO MAKE A GOOD SKETCH OF THE WIRE CONNECTIONS...turn the power off to the unit and the furnace/ air handler inside when you replace the wire.
I need more data on the other issue, the unit going off on 'high voltage'... or by that do you mean just this blow 3 amp fuse.
We can go from there. I will be in for another hour or two tonight, then back in the morning. There are no time limits here.
Thank you for the positive rating!