Originally Posted by Sigma
Well my dad brought the car to a mecanic, sadly enough the mecanic is looking through books trying to figure it out (kind of sad)
It'* acting very much like a bad ground, especially when operating one device (e.g. the horn, in this case) has an effect on other devices. This shows that current is not flowing in the directions it should be going, and is instead seeking a ground path through other circuits.
Have your mechanic start by checking every ground connection he can find, starting with all the battery cable connections.