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2005 Hyundai Sonata - Horn problem

car had been sitting in driveway for a month when the horn( not the security alarm ) started sounding solid. unhooked the battery and the horns . the doors unlocked during this episode… reset alarm and one month later the battery was down to zero. Obviously have an electrical problem but have no idea where to start

First you need to have your battery charged and tested. Replace if necessary. Then it needs to have a parasitic draw test to determine if there’s any unwanted draw from your battery while sitting.

That’s a sign that the BCM is starting to fail.

Tester