Pulling hair out over wiring!

[Paul Frog]

I have a 80 2 wheel drive, that's got a wiring issue bad. Gotta use another truck to start it. Once started its fine, but don't shut it off. It will not start or even attempt to turn over. So, I took my little meter and unplugged the battery checked my fuses. Found a short in the horn fuse. Would that really cause this hard short? The book that I have is junk for wiring we know the type, Haynes! What else does the horn tie into? My dome light wont come on with the fuse pulled. I just don't believe that a horn will cause this much problem. Any advice from anybody will help out tremendously!
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