Is the positive power cable to the winch burnt through the insulation anywhere?
I'm trying to get a clear picture of how the current went looking for ground through the brake lines. It's clear that it did, but the melted positive terminal means it should have lost power as soon as that melted, so somewhere else is probably where it lost ground and then hunted it elsewhere.
We had an ambulance with a 270 amp alternator lose the main ground and when that amperage went looking for ground, it fried every switch, solenoid, and relay in the vehicle.
I'm thinking your positive isn't the issue at this point, but the ground side is what caused the issue.
Can you tell where the leak for the brake fluid is from or was from? The lines go into the combo valve and that needs to be opened and inspected to make sure none of the moving parts are arc welded to the block. (not a proper weld because they are brass and the block is aluminum, but the arcing could stop them from moving correctly)
I am Savvy
Knowledge does not equal understanding.