[Superman]

I think the fat red wire is directly connected to the battery. If the short is at the alternator end of that wire, then current is going to ground. There seems to be only two ways it can do this. It can go to ground using the brown (ground) wire or it can be shorting directly to the fan housing via the alternator case. With the alternator in situ and all wires disconnected, then test for resistance between the upper left and upper right terminals. If this shows infinite resistance, then test between the upper left terminal and the case of the alternator. If this also tests infinite resistance, then your alternator is not shorting the red wire to ground and if your system has a short, it is located somewhere else.