They are pronounced in exactly the same way, regardless of the speaker's accent. In fact, they are the same word. In the past, people would blow on an animal horn (such as a long sheep's horn) to make a sound that would travel a long distance to warn other people of their presence. So the word 'horn' entered the English language with this meaning. And when mechanical and electrical 'horns' were added to vehicles, we carried on using this same word.

The words are pronounced the same. WE know which meaning is meant according to the context.

There is no difference in pronunciation.