Here are a few things to check real quick. Ground strap from chasis to motor. Battery Ground, Battery Positive .Clean both of these very well and the terminal posts if cables corroded replace. Do a load test on the altenator if ok up to there then check the electrical coupler from alt. to wire harness this coupler gets very dirty from time to time and needs a good cleaning. If you still have original wiring this may need replacing also. If it is OK there and you still have a short then prepare to remove your dash and hunt the problem down there. I have found it is much easier to work on the electrical system inside the car after removing the dash just be careful not to damage anything as you pull it out. Most of electrical system will come out with the dash! Could just be a bad ground there. A good continuity tester is golden in these instances. Hope some of this helps it is exactly what I had to do. Good Luck!
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