1995 Chevy Van Battery drain

My Chevy G20 conversion van's battery drains low after sitting for 2-3 days. Performed a system check with a test light by pulling a fuse at a time and found that the one labeled Horn/25 amp when re-inserted caused the light to come on indicating a short in that circuit. A HaYnes or Chilton book shows no diagram for this wiring circuit.
Question: Can anyone tell me how to find where the short in this circuit is occuring?
Also, what may be part of the problm!
My gas guage shoes full all the time! (Wish it was)
Could this be on the horn circuit?
Wher can I get answers and maybe a wiring diagram showing this problem? Much thanks.