I'm not sure you can deduct interest on a loan used to buy a second personal residence, unless it is secured by that residence.  

It's not unusual for taxpayers to borrow against their personal home in order to buy rental property, and in those cases the interest is generally deductible as a rental expense.  It is unusual for taxpayers to borrow against a rental property in order to buy a personal home, and I think that's because they later find out they just stepped in it.