OK you're getting somewhere........ One question, do you have the orig alt or a new internal regulated one?
If it's the old alt...........the voltage reg has a ground via the housing base and a wire (if I remember correctly)........ unbolt the reg from the fire wall and disconnect the ground wire (if it has one) reinstall the hot wires and see if you still pop the fuse....... if you don't..... I'd guess the reg has gone south. Now if it were me I'd put a new internal regulated alt on it and do away with the old reg. You can leave it bolted to the firewall and hook dummy wires to it, if you want the orig look etc...... In my 67 I did the swap and it solved all the dim, blinking headlights, tail light problems, heater etc...... and the reg problem.....lol