Here is something you could try to isolate the problem. On the left side of the GI fuse there are a bundle of GI wires soldered to the fuse bracket. Unsolder the whole bunch and then with the power on and a new fuse installed, touch each wire to the fuse holder and see what lights up. The area with the short won't light up and will blow the fuse if you hold it there very long. That way you'll know the general area where the short is and this will help you find it. My guess is that possibly a screw touched a wire and grounded it or you have a shorted light socket. This method will help you isolate where the problem is. Best I can think of.