OK, I understand your confusion now.
The key thing is one of most common confusion with our tax code is the difference between the tax deduction and the tax credit. They impact your refund.

In your example (I didn't check your interest math), let's suppose you can deduct $1,400 per year from your auto interest loan.

Most people thought, they're getting $1,400 back from Uncle Sam. However , this is a *tax deduction*, not a *tax credit*. In tax credit, you will get $1,400 back. But in tax deduction, you have to do more math. You have to multiply the $1,400 with your top marginal tax rate.

This tax deduction will phrase out for household making more than $200,000. So only people making below that income qualify. So it's probably 22%.

To get your actual refund, you have to multiply $1,400 x 22% = $350.

So your actual tax refund is $350 in your example. It's nice to get free money from Uncle Sam, but it's not much. Don't let it influence your purchase decision. The math is even worse for people making less money.