1975 Duster Restoration Project - Freebie!

so far I have changed the alternator, voltage regulator, and battery(all brand new), but I've gone through 3 VR's, they work for about 15 min. and then burn up. I don't visually see any wires grounding out and I'm starting to go crazy not being able to figure this one out. I've checked lots of connections for corrosion, and cleaned a lot of connections...hmmm