Anyone know why horn/ alarm goes off by itself? Is it the horn relay?
where is horn alrm relay located??

help!! itll start making angry neighbors

 

UHFB #36 (fuse) #74(relay)

 

In another vehicle, not an H3.... the horn would randomly go off occasionally. Maybe once a week..... Turned out to be a bad door switch, that made the vehicle think the door would open up, even if it was just parked, sitting there for hours. It was the right rear door, which was the door that got used least. You'd think it might be the one that got used most. A new door switch was expensive. But you could make short jumper out of about an inch of wire, open up the wiring connector in the door jam and put it into the correct two pins.... the alarm didn't randomly go off after that. The vehicle thought the door was always closed, even if it was open.

 

if you have a key fob i would make sure the button pads where clean with some rubbing alcohol maybe the panic button is a bit cruddy.
also a low vehicle battery can cause random issues as could the crappy azz factory battery terminals if you still have them.