What are the Laws Regarding Train Horns?

I bought an old Ford truck a few years ago that I had to have towed to my house.  I found it for sale in the newspaper and travelled aver five hundred miles to see it.  It was parked in an old barn and wouldn’t even think about starting.  I only had to pay $300 for this 1946 beauty.  I have done a fabulous job if I do say so myself and am almost ready for a lengthy road trip.  I want to install one of those train horns that I have seen advertised, but my wife is making e check the laws first.  She is no fun at all.