If you deactivate the horn your car will not pass the state
inspection next time. In order to get rid of the problem you have
to reprogram the alarm system. For that you have to find out which
alarm system you have. If you have an aftermarket alarm system then
you can check the alarm system manufacture website for
instructions. If the alarm system was installed by the manufacture
you have to contact a local car dealer (the same manufacture of
course).